hogwallow

Well here it goes. I have an 81 K5 with a bad motor. I pulled the motor, tranny, and t-case as one unit and put in a 350, 700r4, and t-case unit in. They were both running units, the 305 in the blazer and the 350 from the truck. I installed an intake manifold and a new distributer from msd. the street fire. I started the engine to set timing and it ran for a few seconds then died. I put in a new starter thinking there was not enough voltage at the dizzy, was getting around 8. With new starter was getting 10volts while cranking at dizzy. Still no spark. Put old dizzy in and still no spark. Put msd back in and still no spark. Replaced mod, Still no spark. Replaced coil and still no spark. Frustrated I walked away and truck sat for 12 hours. Tried to start and it fired right up ran for 30 seconds and died and then there was no spark. Checked fuel pump it was fine I am getting power to coil with key on and while cranking, Ground wire to block is good,I have ground at block, frame, body and dizzy. Took wire harness off and wired up just the dizzy, starter and altenator, Put in new accel dizzy and still no spark unless it sits for 12 hours or so then it will fire and run for 30 seconds then dies. and it has had new wires and spark plugs from the start. So does anyone have any ideas on this one. Any help would be great thanks