Frank,
You are remembering only part of the early days,lol
You can put a "late L Six" or a V8 for that matter in an early truck
They both have the same bolt pattern,but ya gotta change out the rear crossmember.
Up thru 53 on the trucks,the mount pad surfaces on either side of the bellhouse was virtually Flat i.e. parallel to the ground.
In 54 the mount system and bellhouse changed to have a 2 piece sleeved thru the bottom bevel/angled mount.
To put that 292 in Your 50 you need IDEALLY a 54/55 1st series crossmember,which will bolt/rivit directly in place of your old one.
OR as a second choice a 55/72 truck crossmember.
It,ll have the right angle on the mount pads, but I,m not sure of the frame rail width and/or if its the same as the A D Trucks.
Obviously You are gonna need the correct GM corporate bellhouse to match that engine,
cause the bell of your old 216/235 is TOTALLY Different.
Regards,
Steve Sr.