Picked up an inboard-outboard setup from a donor boat (20' Mark Twain)

The stern drive, a 1976 mc-1 (pre-alpha)

The motor 1976 Mercruiser 888
Which is basically a Ford 302, with 351w heads, and 351w cam from a truck or rv
Rochester 2-GC carb
Customized for Marine distributer, cooling systems and manifolds
(Sorry messy shop as always)

Having a hard time with this motor though. It's caused me all sorts of hell.
The starter was stuck, the carb was corroded and all butterflys were stuck/frozen.
The centripical advanced distributer was stuck and points corroded.
The block was cracked, but I had a replacement. which afterword I dropped the one I replaced on my foot.

.
Now working through timing issues, been trying to put it off, but I might need to take it partically back apart. It looks like I might not have the cam timing right.
In IRC we started talking about possibly setting this up as a propane powered boat.
Working out the numbers, it would not have a great run time per 40lb tank, but for my needs it would work fine.
The properties of propane in this application are.
There is no trouble of varnishing tank and parts in the long winters we have.
The fuel stores essentially as long as I would ever need it to.
The oil would likely last much longer.
Oil changes are never to much fun in this kind of boat.
Simplicity in carberation, with nearly the gains of EFI, without the complexity and troubles.
Predicted drawbacks are:
A minimal loss of power. This setup is overpowered in this boat so maybe not a noticed drawback.
Cost of fuel is a bit higher
tank options and space are limited, as well as fuel capacity.
Loss of Coast Guard certification, but not enforced to any real degree where I live.
Anyone have any other pros/cons to propane conversion?
Also i would like to document here what that conversion would take.