My son-in-law had the same problem with his T-bucket. It was the distributor. He had it recurved, and it worked fine. However, if your distributor is new, the curve is likely close.

Are you SURE you have the distributor installed correctly and all the spark plug wires in the correct order: 1-8-4-3-6-5-7-2, clockwise?

Bring the engine to #1 TDC. On the distributor base, mark the location of the #1 spark plug tower. Pull off the cap and make sure that the rotor is pointing at that tower. If it's not, the distributor is not installed in the correct position.

Also, 4 degrees BTDC sounds pretty low for initial timing. Have you tried kicking it up a notch or two? 12 - 18 degrees is not unusual.