Captain Obvious

If it's not to late... Don't pull the housing. If you have concerns about this being the issue, pull the valve cover and look down along the back side of the chain guide and see if the tip of the bolt is pushing against it. I wouldn't mess with the thermostat housing if you don't have to. They're too prone to leaks to mess with unless you really have a compelling reason to do so. And besides........ The chain guide backing plate is steel, not aluminum. If the stuff you found in the pan is non-ferrous, then it's not the metal from the chain guide.

Excellent!!

My understanding is that the reason exhaust valve seals are less of a concern is... The cavity where the valve stem passes through the exhaust port is never under vacuum like the intake port area is. It's less likely you would ever pull oil INTO that area because you just don't have the vacuum differential like the one you see on the intake side.

Here's some pics from an early 260. Maybe these will help?

Remember, he's living on an old hammer farm and apparently they grew in the field out back. The later you pick 'em, the bigger they get.

Chrome.

I suspect you're having the same "gas seems to have gotten less dense over the years" kind of level adjustment issue that has affected several owners.

Obviously. That would be reckless.

Well if you did check the oil that frequently and it really IS disappearing, that's unfortunate. I was just hoping it might have been a non-problem. A quart in 100 miles is really a lot of oil. At that rate, I would have expected you to crop dust a mosquito fogging blue cloud behind you. Especially without a catalytic converter.

Gotcha. So there is a leak between the small control connection and the 5/8 connection that goes to the balance tube? But the side that goes to the air cleaner seals up tight? If the leak from the control line to the balance tube connection is a small leak, the valve may work OK. As long as the side leading to the air cleaner is sealed, it won't create a vacuum leak. Give it a try in application and see if you it opens briefly when you let off the throttle. Test procedure is described in the fsm:

25 will run, but it's a little low. I believe the float level for those carbs should be 20 mm down from the bottom of the lid. I draw line on the side of the carb body:

Actually, I don't believe that you must have your hood off for it to be considered hooning, but it doesn't hurt! I think part of the definition of hooning requires an entertaining amount of mostly safe, but moderate risk and recklessness. That recklessness is most often achieved through the application of velocity. But you can also achieve some recklessness in other forms instead, such as missing major parts (like a hood). If you don't have a hood, you don't have to drive as fast in order for it to be considered hooning. I also think that driving a car that has only a handbrake would be considered hooning, even if you followed all speed restrictions.

Are you really sure you lost that much oil? That's an awful lot!! Especially under normal driving conditions. Typically intake valve seal leakage is worst when coasting and the intake manifold vacuum peaks. But under normal driving conditions, that doesn't happen all the time, just sporadically. I'm going to throw out a scenario.... You checked your oil before you started your motor and went on your drive. The level looked good. However, unbeknownst to you, the night before, your anti-drainback valve on your oil filter leaked and some of the oil typically held in your filter drained back into the crankcase. Then you went on your 50 mile drive and checked your oil shortly upon returning. At that time, you found you were about a half quart down. I would propose that it may not have burned away, but maybe just shifted locations? I've seen this scenario occur and just trying to get to the root issue before you go stuffing rope everywhere.

I believe this is what @Zed Head refers to as "hooning" Did I say that right?

So I went back and found my notes. I was aiming for about 9.4 compression ratio. I'm running an F54 block with stock flat top pistons and a P79 head that has been shaved .040.

I'm not sure I understand what you mean by "smaller pipe". There are three connections to the device... One small (1/8 inch?) control connection, and two larger (5/8 inch?) connections. I thought the two larger connections were the same size at about 5/8 inch? That's not the case?

I did calculate it as I designed the concept, but I don't remember the number. I'll dig up my notes and see what I was thinking. I don't think it was in the 10's. I think I was aiming for mid to high nines. I probably should have had that info handy before I posted that pic. Sorry.

I'm no materials guy, but my expectation is you would certainly not want to temper a spring. If the wire is already malleable enough that you could cold form that wire into the spring shape (without snapping the wire because it's too brittle / hard), then tempering would just remove the springiness of the spring. It would be an ex-spring.

Pedantic, but looking at the intake tract, I'm thinking 73. It's clearly a converted flat top system.

I used the rope stuffed in through the spark plug hole method. I didn't trust that my tired old rings were up to the task of using compressed air. I wanted something of positive volume in there. Besides... I work slow. And the rope doesn't care.

Yup. They are all 200-210, and I'm pretty happy with that. That's the motor I have been building (for way too long!) for my 77 280Z. It went around the big country block yesterday!! Then that compression test was when I got back. Looking good so far! I got one cylinder running cooler than the other five, and I'm not sure yet what's going on with that, but I'm pretty happy. I haven't opened it up WOT yet on the road yet. Want to give the rings time to seat without making anything angry.

Yeah. I have no idea what's going on with that antenna connector pigtail on my car. It looks factory, but it doesn't make sense.

Haha!! Unfortunately, that's probably exactly what happened!