Check that you are for sure at top dead center on the compression stroke with the distributor rotor pointing to the #1 cylinder. Make sure you don't have the distributor 180 degrees off. I just got done with my 258 and spent 3 frustrating days until it hit me like a ton of bricks that I was 180 off.
replace your cap, rotor, wires, plugs and coil if you can that way you can rule out any issues with them if you arent getting the timing right.
It would be alot easier for one to determine what the issue could be if you gave more information on exactly what you did to rebuild the motor.
78 cj7, 434hp 350. th400, 2" lift, dana 44s, 32" bfg ats
02 wj dd