I bought a set of 3 screw round tops on eBay. The carbs cleaned up real well, but the drain plug was rusted, and ruined the fuel bowl assembly on both. Anybody know where I can get new fuel bowls?

That sounds a bit strange.

It has been a long time since I fiddled with Z SU/Hitachi carbs. but my SP310 Roadster has brass fittings in the fuel bowl.

Once I got them out I was able to grit blast the innards of the bowl and remove all the nasty corroded alloy and sediment.

If you do indeed have steel drain plugs, perhaps a prolonged bath of WD-40 or similar will enable you to loosen them up.

If the threads are trashed perhaps they can be bored out and re-threaded for a larger plug, BRASS this time:devious:

I don't doubt I could eventually get them clean, but if they are readily available, I would just as soon replace them.