MAN! I don't get on the site much these days, and saw this and thought Mrs. Aquaholic was.....well.....maybe expecting!
Here we're talking about a dinky boat........SO much for YOUR priorities Tony! Get to that would ya?
I think you're going to be fine. More than that, these 12J pumps we all routinely use are really only designed to handle around 500HP (Back then, that was a LOT), so I'd feel safe your 6J can handle a tad more than 70hp. Tommy'll figure it out.
You probably also figured it out already, but I'll illustrate it to the masses, Jet Ski, Wet Bike and Snowmobile engines are almost the same exact thing. These days, old Snowmobile engines from the north are a dime a dozen................. JIC any of you want to duplicate this thing Tony is prolly gonna finally hurt hisself in............
Ray