Re: will a '69 jet pump fit a '73 short shaft.
Are the engines both short shafts? On the Jet pumps the only difference between short and long shafts is the length of the drive shaft, and a GOOD shop can cut and weld the shaft to change the length.
Outboard Jets makes all pumps and no longer lists the old low horsepower engines. They have a web site and might tell you if you call. I had a 20 Johnson with a pump years ago and I think I remember that there was a good range of years that would interchange.
As I remember the 30 horsepower and up Johnsons use a different pump housing and will not interchange. Not sure about the 25hp engines.
Another issue is the impellor size. The 18 hp uses the smallest impellor and I doubt they are still made. If the impellor or housing wears too much the unit is very hard and expensive to properly rebuild.
You lose 40-50 % of the power with a pump and the small engines will need a very light boat--about what you would normally put a 10hp on.
