Racing Fuel Systems

While browsing at a flea market last week, an old Holley 390 carb (List 6299-1, 4160 vacuum secondary) followed me home. It was only five bucks, so why not

Anyway I stripped it down today, removed a buttload of mud dauber wasp material from every bolt hole and vent tube, and it looks salvageable with a good cleaning and a rebuild kit. Tiny main jets (#50) and really little PVCRs...

There's a little rust on the secondary throttle butterflies which I'm tempted to bead-blast after removing them! and the shaft is rather stiff. The main body is surprisingly clean inside although the gaskets are petrified wood. The secondary vacuum pod actually moves and doesn't leak, too!

The bowls and metering block are soaking in my gallon can of "Berryman Chem Dip". But it needs a special screwdriver to remove the metering plate screws - the tip is shaped like an "8". I've never seen one like that, are they hard to find? Edit: It seems to be called a clutch head screwdriver, 5/32".

It looks like a 37-1542 rebuild kit will work, or the aftermarket equivalent, although that's $40
Anything special I should be watching out for? Other than an engine small enough to need a 390

It's called a clutch head screwdriver. There might be different sizes .

I finished disassembling the carb tonight. Someone's definitely been in there during the last 50 years or so...

One thing I noticed was there were four white nylon split bushings on the secondary throttle shaft, but none on the primary.

The exploded view of a 4150/4160 at https://documents.holley.com/techlibrary_4150_4160_exploded_view.pdf shows four for the secondary, ok (it's part 190 on the diagram) but the key says "Throttle Shaft Bearing (Ribbon) Primary and Secondary". And one solid bushing 189 for the primary shaft.

I've never taken one completely apart before. Anyone know if there are supposed to be "ribbon" bushings on the primary shaft too?

Secondary shaft of vacuum carbs only. They are in the kit you referenced. I have never seen 189 on primary shaft , and I have done a lot of Holley carbs . Unless it is referring to a spacer.
The clutch screws can be removed with an appropriate size flat tip screwdriver

I have used reduced thickness teflon/nylon bushings on the primary shaft to repair a loose shaft .
You can also buy thicker teflon/nylon bushings for the secondary shafts when the baseplate bore has worn larger.