Here is a source for mostly O470 GPU stuff. Many P/Ns same same as
certified AC parts. Ducarra aviation.
When I worked for Uncle Sugar we found that the GPU O290 ring sets
were the same P/N as the aircraft engine ring sets. About a $60.00
difference in price.
The airboat outlets have many GPU parts sources as well. Try "Outlaw
aircraft engines". Does real aircraft overhauls. Sometimes very good prices
on Overhauled and yellow tagged cylinders from a FAA licensed
shop.
Lynn E. Hanover