Hoyt,
The '65 C10 manual shift 1/2 ton truck was originally made with engine and bellhousing mounts and no mount on the transmission. It was also built with with a cast iron case manual transmission designed for use without a crossmember.
What makes this different is a Muncie aluminum case transmission is being used that was designed to have a transmission crossmember.
It is my understanding that if the truck came with an automatic transmission the factory installed a transmission crossmember.
Anybody know if the 55-57's Chevrolet manual shift passenger cars used aluminum or cast iron case transmissions?