I dimly recall that cletis has been using a disguised electric fuel pump in his truck (for several years). Maybe he'll offer suggestions/information?
In terms of "size" pumps, you need a gallons per second number.
1958 Chevrolet trucks fuel pump ratings (GMC would be similar, I'd guess):
3.5 - 5.5 psi for 6 cylinder
5.5 - 6.5 psi for 8 cylinder
