If you try the 350cfm carb there will not be any noticeable change what-so-ever, don't waste your time and money on one I've tried one and it was a disappointment. The 500cfm carb is a difference of night and day for performance and overall drive ability. In some cases 305 V6's have ran too rich from the 500 but the remedy for that is to re-jet it and the problem is solved. I first did this conversion back in 1975 at the age of 15, I wanted better performance out of my father's 68 KM-2500 (Now mine) there was no aftermarket 4bbl conversion around or anything performance but I figured the 305's 2bbl base was standard GM issue so then a carb adapter for GM 2bbl base would work and it did. The truck was already upgraded to dual exhaust, 16 years later I built an HEI for it. The engine never seemed over carbureted or running to rich and would always pass the California biannual smog test far above average.
