This must be very frustrating to you! We'll get to the bottom of it eventually . . .
I would think 90+ would be plenty good enough to start.
Engine needs 2 things to start: Fuel, and Fire.
Fuel: R U confident the new carb is correct? Looking down the throat, does it Squirt fuel when you rapidly open the throttle linkage manually? When you crank it, does it sound like it's got suction through the carb? Is the fuel you're using good? Some people swear against it, but others will try starting fluid. It's more volatile, will fire easier. (Some claim starting fluid is so volatile it will damage your engine . . . I'm skeptical, but not certain.)
Fire: Sure you've got good spark at the distributor end of the coil-to-distributor wire? Sure you've got good spark at each plug wire? (Point gap is at least close to right? Rotor is correct size? Cap is not corroded?) Finally, timing must be correct. Re-read posts to confirm correct setting. It's REALLY EASY to mind-warp and set the timing 180 degrees off. As 54Tow says, the bb only tells you Top Dead Center of #1. It doesn't tell you if it's TDC on the compression stroke, or the exhaust stroke. You have to watch the valves for that, either #1 or #6, as previously posted in this thread.
A good charged battery will make it easier. I doubt your starter is the issue, unless it feels like it's turning too slow. Are the bat. cables clean and well-attached? Ground clean on the frame? Cable clean and tight on the starter?
Timing is still my guess, but then, I'm usually wrong . . .
Just had a thought: Are you certain your exhaust isn't plugged up? Rat's nest, etc.?
Keep at it - you (and US!) will be so thrilled when it finally starts!
-Michael
