Thanks PPRuNers! Those were exactly the clues I needed to get a start. We're looking at converting an A150L to have an O-240, if it's practical. Having the "other" TCDS is a great start, as that demonstrates that it has already been done. Knowing the parts differences is a help. We'll see where this take us...
Weren't the Reims aircraft also corrosion proofed as standard as opposed to US built units
Correct, that's what I notice when I'm around "Cessnas" in Europe! If you ordered a factory floatplane from Cessna in the US, it came with zinc chromate primer throughout, otherwise they are bare. This has proven to be very false economy, considering the corrosion problems now seriously affecting some Cessnas. My other plane had factory primer throughout, and since its manufacture in 1975, no corrosion whatever. Whenever we do repairs now, we prime the repair parts.