Welcome aboard, Andy!
Cessna factory oil coolers in 150's are rare, as not many floatplane 150's were ever built. I would add one to mine, if I got the chance, but then I'd have to use the Continental oil filter adapter that I don't like (I use the one that replaces the oil cooler adapter). Recheck your logbook entry for the engine installation, and if there's mention of installing the Cessna 150 floatplane oil cooler according to Cessna documentation, then you're probably good to go. No 337 required on at least 1967 and up 150's (1967 was the first 150 floatplane offering).
Lionel, the oil cooler was a Cessna addition, not Continental. If a 337 was required (it isn't unless the airframe is older than 1967), it would be for the airframe, not the engine.
