Here are some old notes I kept on the thermoquad's rods and jets, fwiw. Some of this info is from the 1975 Scout II xlc factory manual. As usual for IH, it included generic 392 engine info as well.
V345, 392, cal and fed: main jet: 0.098", rod 75-2020 has dimensions, in inches, of 0.064-0.052-0.045. As the tq was not offered on the Scout in 1975, I'd venture this was for the p'all series. These are tq #6590s (fed) and (cal) tq #6592s (manual) and tq 6551s (auto).
For the 77-78 345/392 we have tq #9128s. This is likely what you have, and it conforms to what I have documented on scouts with this carb. With the 0.098" jet, you have rod 2273: 0.080-0.064-0.044 (inches). IH list is 490561 c91. Phenolic bowl #2618a. Note that the rod has a slightly larger base diameter - this would yield a somewhat leaner mixture.
The bowls are funny. I last bought a new bowl from tomco around 2001, paid $75 and was glad to get it. A number of different styles are out there to match particular applications, mostly mopar. I will venture that more are useable than you May think, so if yours is trash, don't shy away from chrysler bowls. If you pay careful to what passages IH used, choose an appropriate air horn gasket that will block/enable those passages. Some mixing/matching appears feasible, but you'd have to sort it all out. There was even a mopar application that had an
aneroid That bolted onto the front of that large "flat" on the front of the carb's air horn (air horns for those were drilled and had modified passages). It would lean out the mixture for vehicles running at higher elevations. Geee...
that Has possibilities.
In short, if you have an actual Scout tq, and the bowl isn't too warped (can be fixed), and you can get brass floats - new nitrophyls if you can't, and the rods aren't too worn, and you get those teeeny air bleeds clean, and can put it all together "by the numbers", and fix any vacuum leaks caused by the manifold to carb gasket and related vacuum hoses, you should be successful. But you'd do this all anyway for any other carb, so this isn't really any different now, is it?
One last tip. When you get to the point of screwing down the air horn with those ten or whatever screws, do it in stages. A light stage to get it just compressed (criss-cross). Walk away for a few hours. Do another light tightening and walk away again for a few hours (I did mine the next day). Then snug up for a final, but don't overtighten and strip. Gaskets will slowly compress between tightenings and give a better set. Don't rush it.
