I got educated on this back in 2008 here on The Stovebolt: https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=451242&page=1

What I learned was from an engineering and stress consideration you ideally only want 2 support locations on the engine / transmission assembly. (front and bell housing -or- front and transmission)

If the engine already has the front and bell housing supports then the transmission should not have the support.

If you are of the opinion that the transmission needs to have a support you should eliminate the bell housing support location.

I did not install a transmission cross member on my '65 C10 that runs a M-21 Muncie 4-speed car transmission and have had no problems with it.

In the Stovebolt Gallery ~~ "The Orange Crate" 1965 C10 SWB Step Side Build Thread

Inspired to be different. Different in a way of my own, not in a way that others strive.