The mods for the end carbs are pretty straight forward.

After you dissemble the carb the first step is to eliminate the idle and intermediate circuits. All I do for this is remove the idle screws and lightly heat the top of the base (usually with a hand held propane torch) and melt acid core solder into the passages. I've done this on all the ones I've modified and have never had a problem with the solder melting back out.

The next step is often overlooked, and that's centering the throttle plates. Normally when the carbs are mass produced the plates are not perfectly centered, it's not a big deal on a normal 1 carb set up as the throttle plates are always open a little anyway, but if they are used as an outboard carb it creates a vacuum leak and is almost impossible to get a good idle. Simply loosen the throttle plate screws and adjust the plate until you have a perfect fit. One thing you might run into is that some of the latter carbs had the plates held in with rivets. The procedure is the same except you will need to drill the rivets and tap the throttle shaft for plate screws.

As far as the power valve normally I jet the carb down a little and leave the power valve functioning. If you find that this is to rich, simply cut off the spring loaded rod that's in the top of the carb. Do not pull the whole rod assembly out of the carb top as it will create an internal vacuum leak. As the power valve is normally closed and the rod depressing is what opens it this effectively eliminates the circuit.

From my own experience, 350 CI is kind of a grey area as far as the small base 2GC is concerned for a primary carb. The small base carb works well under 350 CI and in most cases on stock 350 CI engines. On larger engines or modified 350s they seem to choke the engine. Normally in this case I use a large base 2GC as the primary carb. This requires making an adaptor plate to make up the difference in the bolt patterns. I usually use a 3/8 piece of aluminum and recess the screws to hold it to the manifold and then drill and tap for studs to hold the carb. I then use a die grinder to blend the ports. While the majority of the small base carbs have a side inlet for fuel the large base use a front inlet. In some cases the carb spacing is such that you can use a 90 degree adaptor but in others you will need to modify the fuel inlet. In those cases, I normally remove the inlet fitting (the large one that holds the fuel filter in) and braze the inlet closed. I then drill and tap for an 1/8" pipe fitting in the side of the housing. As the Large 2GC is a little taller and then the adaptor plate is under it, I raise the outboard carbs by simply using the thick base gaskets normally found on the late 70s applications.

The final thing will be dialing it in. I have yet to find a source for off the shelf jets or power valves. The jets that I have come across have run from 43s to 52s. The good news is that jets and power valves are interchangeable between the small and large base carbs. The small jets are found in the carbs used on some of the early 70s V6s and the larger ones are found in the large base 2GCs (2BBL Pontiac 400s are a good source for 52s).

Hope this helps, depending on how much modification you do it can be a little time consuming, but if your doing your own work it's really not expensive (your main cost will be $10-15 dollars for a rebuild kit). I really love my tri-power setups, once they are dialed in there just about maintenance free and there's nothing like the feel or sound when everything opens up.