Bought it off the original owner, a navy diver had the boat built by radon to his specification in 87. Shipped it to south Carolina where it was outfitted with a Armstrong bracket and two Yamaha 200's
Engines are gone planning on installing 2 f250's
If those are your two choices I would definitely go with the Cummins, it's a big project to repower a boat. You might as well replace tanks while you're at it. You will also have to replace the 1 1/8" shaft that came with your boat
My boat has a straight shaft, I have owned a 25 farallon with s Cummins it was a incredible boat never had any issues with it, the yanmar is pretty much a drop in replacement for the 454 that is in the boat now and quite a bit lighter than the Cummins. Check out the yanmar 8lv pretty impressive...