Fish,
Here's some more dimensional info for your studies. In the first picture
http://i188.photobucket.com/albums/z...tclrncmeas.jpg, you can see that the 25" V-6 E-Tec on my 30" bracket has about 7.5" of horizontal clearance with the filled in transom, to which I have added a rub rail that sticks out about 3/4". I could therefore get by with a min setback of 22.5"; these motors have an adjustable tilt limit switch, so you could go with an even shorter setback if you used that. A V-4 115/130 hp E-Tec would need even less setback, maybe 18-20". When mounted on a bracket, those motors will push a 20' hull to at least 40 mph, and they're about 30 lbs lighter than the V-6, so if you're not a speed demon they'd be an excellent choice for a bracketed 20. The V-6 is overkill unless you run with extremely heavy loads.
Here's a side view of my rig with motor at full tilt on the 30" Hermco bracket.
http://i188.photobucket.com/albums/z.../Fltltsdvw.jpg As you can see in this picture, much of the powerhead is actually above the transom, so the horizontal dimension to top of powerhead I quoted above is actually quite conservative. If I had a shorter bracket, the top of transom or rub rail would actually contact the motor about where the decal is on front of cover. I have since raised the motor another inch from when these pictures were taken, so I now have even more clearance than shown. If you'd like more exact dimensions at the current mounting height, let me know and I'll go take some more measurements.
Denny