? Engine swap Rotax 100 for 80

[shortfielder]

Some have recommended that the best plane for my mission would be the Model 4 classic, long wing, 100 hp.

All of the Model 4's that I have seen sofar have been 80 hp.

How big of a deal to swap out a 80 for a 100.

Seems the 80's have 2 blades and the 100's 3 blade so ya have to change the prop also.

Would a used, low time 100 be readily available, and what would you expect price wise.

What could you get for a low time 80?

What could I expect to gain in cruise speed w/m4-100hp-long wing?

Thanks again Gary