I had this issue with my '61:
Just put a "new" (to me anyway) 292 in it, cranked slowly also
..... comp test: 90-125 not great, but good enough to start.... a friend was cranking it one time when I saw the throttle pedal twisting back and forth from pumping the pedal was arcing to the body! Turns out the (-) battery cable stopped at the firewall.
I installed a 1ga battery cable from intake manifold to the stud at which battery cable terminates on firewall.
Fired right up like every component was new
Running on the other hand.......................