My understanding, smaller diameter converter has a higher stall speed but also more efficiently transfers the torque to the trans. Generally converters get smaller as the stall speed goes up. When you get a converter the proper way is to call a known good converter company (PTC and Dynamic are two off the top of my head) and give them the full setup of your car including engine specs, trans type, vehicle weight, rear gears... and they will custom-build a converter to match your combination which will perform the best.
What you described about checking the cam timing doesn't really make sense to me, they basically told you just to change the spark timing but didn't bother to reset the sprockets so the dots lined up? WTH? If the timing chain is off a tooth usually it will cause all kinds of issues, least of which is inaccurate ignition timing. If you put a degree wheel on the crank with a dial indicator measuring lift on one of the lifters you can get a pretty close idea of what the duration numbers and lift of your current cam are.
I'm betting those 2.71 gears are putting way too much load on the engine and with decent compression/cam it really doesn't like it, hence your pinging issues. 3.55 gears will take some load off the engine and allow it to rev up quicker which is what the engine really wants to do. Tall gears feel the same to an engine as a heavy vehicle, i.e. with 2.71 gears in a 3200-3600 lb. car your engine is feeling the same load as if it was in a big 5000-lb. truck with 3.55s.
I wouldn't worry about vacuum advance for now seems like you have plenty of other things to fix and mess with...
