R/R engine, now it won't start.

[megaladon6]

the car ran fine then i had to pull it to check the bearings. i changed the bearings, oil pump, and oil pan seal.
when i got everything back together and primed the engine it fired right up and ran for a few seconds. that surprised me so much i turned it off (whoops!) but after then it won't fire. when i first turn the key it fires and almost starts. but after a very short time it stops firing. it gets so bad that it won't do anything, even on starting fluid.
i've played with the timing, reversed the distributor (caused backfiring so i set it back), lowered the float (q-jet), tested the compression (150psi), have spark at the plugs.
i'm out of ideas of what to test. any and all advice is really appreciated.