The clunk in the passenger side rear suspension turned out to be a result of me not having tightened down the nylock nut on the top of the strut. I remember now that I didn't do it because I thought I might have to take it off again before getting the car back on the road and I didn't want to have to replace it. Neither side was tight enough, but only the passenger side was clunking. I tightened them up and the clunk is gone! In fact I've never driven a Z as quiet and (relatively) well-behaved on rough roads! If anyone happens to know the torque spec for those nuts on KYB rear shocks, let me know. I dug around a little, but didn't find anything.
The TachMatch was shipped four days ago and has so far made it from Seattle to Los Angeles. I guess I should consider that to be progress, but it's not exactly the most obvious route to Toronto. I checked the resistance of the fuel sending unit and it's showing 0 ohms, so I think I'm just going to order a new one and move on. There are some gaps between the hatch seal and the bottom of the hatch, which explains the "richness" of the interior environment. Tomorrow I think I'll try filling the gaps with a towel or something to see how much I can seal it up. The sides of the hatch seem to be well sealed, so I'm not sure why the gaps exist at the bottom. Both hinges are interfering with the top of the hatch seal, but I'm hoping the exhaust isn't getting in up there. Slowly, but surely ...