Not an expert but my old 67 Special with a 300 had a th350 mated to it by the previous owner, so it has to be possible. Worked great too! But don't know what was involved with drive shaft, linkage, etc. He also rebuilt the oringinal 300 w/ 2 barrel with a mild cam and new lifters from Poston and installed a 4 barrel mainifold and carb. I gather that the 4 barrel manifold is getting real hard to find for these 300s now. Good luck.
Performance improves for the 300/2V Take a look at the Jet Electronics 500cfm Rochester 2GC. It's modified to use Holley jets for circle track use. Will need installation of choke for street use. Or you could use a common Holley 5200 to 2G adapter and use a 500 cfm Holley 2V carb. 4V intakes can be found if you don't limit your search to Skylarks and Specials. Look for the big cars in the bone yard. Many of the mid-60s had 300 engines.
Will a TH350 mate without help? depends on the TH350. they came with both Chevy and BOP bell patterns. use this thread to tell the difference: http://www.teambuick.com/forums/showthread.php?t=9781 supposedly, all of the 200r4 transmissions are set up to accept both patterns. some TH350s are also set up this way. you can tell because a dual pattern bell has 10 bolt holes instead of 6.
