We recently sold our '87 Chris 410, which by then was called the Constellation and not the Commander, yet was essentially the same boat. When the original 454s began to go south, we looked at repowering with diesels. Our mechanic reminded us of all the other stuff that would be involved, from transmissions (the old Velvet Drives wouldn't handle the torque of an equivalent hp diesel), to motor mounts (as mentioned previously in this thread), to fuel lines and wiring harness, different props, not to mention that we'd have to change over to a diesel generator as well. We ended up repowering with fresh reman long blocks overbored 0.060", rebuilt Velvet Drives, reman Rochester Quadrajet carbs, and conversation to Delco electronic ignition.
After this repowering work, we had a reliable drive train with a two year/unlimited hour warranty on the long blocks, slightly better fuel economy, and better low end torque which helped in locking and docking.