I'll keep this short, I've got to get to work.
The Reims 150's are certificated under a different type certificate than the Cessna aircraft, therefore, technically, they are a different aircraft. Generally its not a problem, but many (should I say most) STC's for the Cessna 150 specify the type certificate number 3A19 on the front of the STC as the applicable aircraft. Unless the STC specifically lists the Reims TC, which is A13EU, then that STC cannot be applied to the Reims aircraft without going thru the field approval process. Probably a simple paperwork drill for most STC's, but still a hassle to deal with.
Also, parts are difficult to find for the O-240, Continental supports the engine but not very well. RR turned all support over to Continental several years ago. Many Reims Aerobats have been converted to O-200's due to the lack of O-240 parts. (heresay on my part but I have no reason to doubt that)
Charles.
Charles