By now I get the overwhelming idea to replace these Zeniths! That's on the "to do" list, but a little further down the financial road. Have made some improvements that I should have checked from the get-go. Firstly, there was a crack along the brake vacuum assist line so I replaced it. Secondly, I found a small vacuum at the base of each carb. Problem here was only 3 gaskets in the rebuild kit and 4 possible places to put them (between the spacers and heat shield from the throttle body to intake manifold), so I made my own - cured the leak even if it's unorthodox. Thirdly, and I don't know how, the timing was too far retarded by about 2 degrees. Fourthly, rechecked the carb covers and the front one was just slightly (I was picky here) off-true, so I re-sanded. Fifthly, balanced the carbs yet again. The above brought me to about a 75% improvement with much better acceleration, but still sluggish past a certain acceleration point, some backfiring, and poor fuel economy. I'm going to check the valve clearances this weekend and, depending on what I find, do a compression test (probably will test compression anyway just so I can sleep at night). I feel that I'm almost there and I couldn't have kept with it without all of the support you guys have given - I'll keep you posted!