If the engine is running fine why to repower it? Even if it is hard to find parts, if running fine it won't cost you a penny and you will be able to repower it the day it brakes, if ever it brakes.
My boat engine is even more exotic than your perkins but works like a charm and I would bet I will die before it. The only parts I need for now are things like oil filter, fuel filter, oil pressure sensor etc that are not really engine related and easy to find.
Just a thought