First, all v8 hydros are out of trucks. I suppose there are some industrial applications as well, but no passenger chevy passenger cars came with hydros.
Second,all 1/2 through 1 ton trucks, (light trucks), had an open drive shaft. Therefore would have a seal for a drive shaft slip joint.
So those are out of the way. The trans in your pictures shows some type of flange that is most likely for bolting to an auxiliary trans or to a closed drive shaft system.
It appears that there is a tag on bell housing in the third picture. If so that could be of help.
I would post on the big bolt page and see if someone has seen this arraignment.
