There certainly are a lot of fasteners between the bellhousing and the iron block! I have the FiveSpeeds bellhousing with same bolting as the OEM automatic trans.
It gets weaker with the 4 bolts into the threaded holes in the aluminum bellhousing to transmission connection. That's where I would be concerned.
There were steel brackets on horizontal surfaces at the back of the block, which provided additional bolt-and-nut connections to the bellhousing. Adaptation of these would seem a possibility.
Of concern to me is that when I saw my 4.2 in the chassis, with no cushioning (metal on metal at the engine mounts) there didn't appear to be any space at the cowl to raise the engine at all.
It gets weaker with the 4 bolts into the threaded holes in the aluminum bellhousing to transmission connection. That's where I would be concerned.
There were steel brackets on horizontal surfaces at the back of the block, which provided additional bolt-and-nut connections to the bellhousing. Adaptation of these would seem a possibility.
Of concern to me is that when I saw my 4.2 in the chassis, with no cushioning (metal on metal at the engine mounts) there didn't appear to be any space at the cowl to raise the engine at all.