Hi I'm new to the board.
Don't know where to get started on this I'd like to build a Mud motor from the outboards and 4-stroke motors I have. I have several outboards with blown power-heads.
Several vertical shaft commercial grade Briggs engines with electric start.
4hp -17hp-16hp and a horizontal Kohler magnum 16hp.
What I want to do is mount the 16gp Briggs on a 15hp rude short shaft.
I've seen these on utube using smaller engines.
I would also like to extend the prop shaft 24" then add a 2 blade mud prop.
That would give me a aircooled 4stroke with reverse and electric start.
I'm looking for suggestions on mounting the 4-stroke,mating the shaft to the drive shaft on the lower unit.
Also extending the propshaft. I could post my build along with pictures and cost of project.
Has anyone built such? Is the the right board for such a project?

It has been done before.
Dont know how good it worked but I think there are better options out there.

I would say get a motor for one of the major manufactures, Pro Drive, gator tail, mud buddy, go devil.
If you are set on building your own there are plans on the internet for both surface drives and long tails.
Do a search on MMT for “homemade” and you should find plenty of info.