534 used an SAE pattern bell, if what I've read here is correct. The Cat engine would do likewise.

Ratios? The 534 was good for what, 3400 rpm? It probably "cruised" at 2000-2500? Where is the Cat happy?

This would be a fair amount of work, with fuel system and accessory drives part of the little things after mounts and trans adaptation. Regearing could be a deal breaker. Perhaps a different trans with OD ratios would be a better thing to research.

I take it this is a hobby truck and they're not waiting for you out on the fire line, so look long and hard, make lists, check 'em twice.

Check this site. You may still go Cat, but you may get some ideas looking at their kits etc.

fordcummins.com - Increase Horsepower with Ford Cummins Diesel conversion kits