mshaw,
I thought of that like MBHD, 26 sec or 21 sec 0-60 are kinda slow. But, your speedometer could be wrong or just "lagging" when accelerating, that is common with the old ones. So what you think is 0-60 might really be 0-70mph. But at least if you do it the same each time you can measure the improvement.
I took a crack at your car in the Gonkulator, that is tuned to match my own runs with a 63 Nova, stock 250cid 4bbl, 3.08 powerglide. That car ran 0-60mph in 11 sec give or take depending on the carb and timing. Your car is probably 200lb or so heavier, and has 10% less engine so should be slower, but the Gonkulator said about 13-14 sec for 0-60mph for your car when tuned right and if the engine is not too tired. Again, you may be measureing 0-70mph for all we know!
Timing of 2 BTC seems kinda doggy, but you should also check the whole mechanical curve - unplug the vac advance, degree your damper, and check timing vs RPM up to say 3000. Mine liked about 6-10 initial, and 32-36 total mechanical at 3000-3500. Anything close to that would run pretty good. From the hesitating and backfiring I am guessing your timing maybe retarded.
The stopwatch thing is a great idea, been doing that since the 1970s (my old-tech stopwatch from 1974 still works!) but mostly use the GTECH now. Or, the iPhone has a cheap app called Dynolicious that is not perfect but might be helpful for what you're doing so far.
Good luck and keep at it!
FYI, even if that 21-sec 0-60 time is accurate, you could still put the hurt to plenty of cars, including most stock 1953 Fords, and just about any early 144 Falcon or 170 Comet Fordomatic. Well, maybe we need to improve things a little...
