My 63 d100 was slant six with an np435. It used the bellhousing crossmember mounts.

When I went 440/727, I just used a rear crossmember from an auto truck. I cut out the crossmember at the bellhousing, and used factory connectors.

So in my experience, stick trucks had the mounts at the bellhousing, and the tail of the trans just flopped in the wind.

Auto trucks had a mount at the tailshaft.

I did end up using my /6 motor mounts for the BB swap.

I have seen the pancake style mounts used though, I have never done it like that myself