Electrical problem

[ratrod67]

Having some trouble and need some advise. I have a 69 and I installed a 350 and auto tranny I pulled from a running and driving 68 Impala. The truck had a running and driving 307 and 3 speed. I just pulled and swapped them. No changes to either motor. Now I can't get the 350 in the truck to start. When I hit the key it just clicks at the starter a couple times and then stops. I took the starter and got it checked and it was good. I checked and replaced the battery cables and wires to the starter. Still the same. I bought a new(not rebuilt) starter and installed it. Still just a click and no start.
I made sure and triple checked everything. The chassis is grounded and so is the motor. I'm getting power to the starter but I just get a click. I even installed a 3rd starter just to check and still nothing. The 350 has an HEI and the old motor had points. I ran a power wire from the HEI to the fuse panel and I'm getting a full 12 volts to the dist.
Any chance it might have something with the neutral safety switch? Any other suggestions? Thanks for any help...