Here's a kind of "how-to" for putting a 1650 ci Rolls Royce Merlin V12
in a '55 Chevy:
http://www.rodshop.com.au/project55p3.htm
It looks like quite a few "smidges" are required, in every direction.
The Roller might be down 60 cubes to the Allison in that digger, but
the twin blowers and 3000 hp will probably make up for that. This car
has also been street driven. That Allison car, I doubt it.
180 Car