We build a good many of those here, even though I don't advertise for them.
There are several modifications that we do to them to improve performance.
Seldom do they need shaft bushings, and I do not recommend pulling out the shafts unless they are being removed to plate them.
The biggest show stopper for the 2GC carbs are the accl pumps, the over the counter stuff is junk. We sell pumps for them with the good seals and custom wound springs, etc.
I also modify the accl pump system and eliminate the feed to them from the fuel bowl and the aluminum ball under the spring. Very bad idea and most of them leak back to the fuel bowl when the accl pump moves down due to problems in that area.
The center carbs idle system is modified much like a q-jet, but the parts are not the same when it comes to idle airbleeds, idle tubes, etc. There is no idle bypass air system, so the plates need holes put in them for bigger than stock cams or low vacuum at idle scenarios......Cliff