Jerry - I didn't work on my first triple YH set-up until the mid-1960's.
I never had a dyno at my disposal, nor did I ever do a back-to-back run against a single carb so cannot make a comment on performance gains; but my customers were quite happy with the rebuilt system.
Horribly expensive? YES!
Nightmare to keep in tune? Well, maybe, and maybe not. Why?
When I did my first set in the 1960's, there were only 3 sources for rebuilding kits: (1) Chevrolet dealer (special order, no one wanted to wait), (2) a parts house handling Carter kits (not in my locality), and (3) the only aftermarket carburetor kit company (not to be named) that at that time had a large share of the aftermarket kit business.
So I bought kits from source (3). I quickly determined that the bowl cover gasket was wrong for the Corvette (it was correct for the turbo Corvair YH carbs and the late 1950's marine YH's), and the fuel valves were the large orifice, solid needle. I cut my own bowl cover gaskets (not the easiest gasket I have ever cut), and surfaced the original fuel valves.
As far as initial tuning, this was a time in my life before I was bitten by the "buy American" bug; I tuned hundreds of imports with dual and triple SU carbs, so the three YH's were no challange.
We had no customer complaints about keeping the carbs in tune. We did receive calls from others, many of whom became customers, that were experiencing flooding issues. The use of incorrect fuel valves will do that.
As in the second sentence in this post, I have no real data, but would GUESS that by far the best performance bang-for-the-buck on the 6 cylinder Corvette would be to swap the dogmatic transmission for a real transmission. While I don't believe everything I read on the 'net, several sites suggest that the powerglide will lose about 25 percent at the rear wheels, where a stick about 15 percent.
Jon
