I guess there could be variations. I replaced a 4154 with a cummins 4b3.3 from TAD. Required no modification to the beds. See beta vs cummins thread .
I think highly of the beta because so many others have said so. TAD is excellent and I am sure if they want the sale
they can provide you with specific advice. I did not have to jack or modify anything to get it to sit in a position that allowed for great alignment.
I think the water
intake is lower on the cummins then the Perkins
runs and everything were near the same. Still I used all new hose lift muffler