It's a cool old truck
ease of finding parts & cheaper parts
premade available bolt in/bolt on parts
GM oil pan has rear sump, no steering issues
like the Ford engine oil pans & sumps {easy fix}
some of the many reasons, among many more
people do the Obligatory Cheby in the old Fords
Hot Rods all started out with some different,
make or brand engines in them
Caddy engines or Pontiac & Buick or Olds, Chryslers
almost any Overhead Valve engines,
were far superior to the flatheads, especially way back when...
I prefer sticking with the proper make "usually"
but I can see & totally understand why people do it too...
With the parts & tech available today, it's not 1955 anymore
there's no reason why
"they can't be built with, a Ford in a Ford" today...
It's still cool...
or Put a Hemi in it
My favorite old car builds are 39-41 Willys
or the Alterds of the Ford 23 T, late 30's & 40's Fiat Topolino's
to 32 Bantams or mid 30's Willys too, especially racecars
with 354, 392, 426 Hemi or BBC's
especially blown & injected, I'd never complain at them transplants
I guess that makes me a hypocrite