Vezo - the 175s weigh a little more than I thought:
E-Tec 175 is 419 lbs (2009)
Johnrude 175 was 375 lbs in '99

Right around 400lbs (+/-) seems to be about the max weight (25" transom) without major modifications and weight shifting. Add a bracket to the 20 and the LCG gets all out of whack, so you end up having to move weight forward (batteries/fuel tank/ballast).

Weight and CG Effects
 

Bigshripmpin & others-
Hey Tim- You usually are a good voice of reason on CSC. I wanted to alert you to this in case you had not seen it From time to time I try to tell folks of my post on "estimating CG shift with heavy engines". I put together an example of a relatively simple way to estimate the shift in CG due to heavier engines, outboard brackets, etc. If one were to use this when a change is contemplated then they can actually test the results with water filled coolers or weights before spending money and modifying their SeaCcrafts. Try searching on "estimating cg" Post#1 on page 3 of 3, dated 9-24-16.

I second Fishstretcher and Bigshrimpin - with my 115hp motor, I am running at 3/4 throttle most of the time, because it will launch my light Seafari hull off the wave tops. And the hull likes weight in the bow - so go lighter motor: the 140 should be great for the 20 foot hull.