The 1953 Fleetwin base gasket is 202518, and the lower unit is Forward/Neutral only. The 1956 Fleetwin/AD-10 use base gasket 304314.
So I’m guessing the answer is no (I’ve never touched either model of Fleetwin).
(found the Fleetwin parts diagrams in Gary’s DropBox, and the AD-10 here: https://johnsonad10manuals.wordpress.com/parts-manual/ )
My notes say 1954 was the first year for FNR on the Fleetwin (using the Johnson CD lower unit)
http://www.omc-boats.org
http://www.aerocraft-boats.org
