Yamaha shaft length

Hi I am new to this forum and I have a few questions. I just bought a used 1990 Fiesta pontoon boat it has been remotored with a 1994 Yamaha 50hp, model #50ES there may be more on tag but it is damaged an unreadable. The freeze plg has # D81950 on it. This engine appears to be borderline on the prop depth. Can anyone tell me if it is a 1994, if it is the proper length for this application. If not is it possible to extend it to 20 inch length, I believe it to be a 15 inch shaft length. It measures approximately 23 1/2 inches from transom to centerline of prop, and it is as low as it can be mounted, I could remove 2-3 inches from transom but any lower an the steering will be in the pod an the bottom of motormount will be below the pod. Would it be cheaper to sell this motor and purchase proper one? The code on tag appears to read 6 H 5.
Thanks Neil74

[boats.net]

50ES is a 15 inch shaft model number. There are not any shaft extension kits for a 50hp motor that I know of.

Well I'll have to admit I'm very dissappointed with that. Really hoped to resolve the shaft length issue as this is a very good running motor. Not sure if it would be a good idea to mount an aluminum jack plate, designed to use a long shaft motor to a short shaft transom. Seems to be plenty of threads saying they were going to try it upside down but none confirming if it did work or if problems.