Re: Repower could add too much weight?
 

Big difference from 115 to 150 - 4cyl to 6 - once you get to 6 they all weigh the same 150 to 200. The 130 Etec in new maybe a very good option if inclined to going new, but I think it weighs in the same as a 200 EFI Merc at 400.

Re: Repower could add too much weight?
 

In 17 years I Have had a 150 Black Max Merc 435 lbs. A 140 Suzuki 2 stroke 380 lbs. A 1998 150 Evinrude Intruder and now have a 2004 Johnson 175 380 lbs on my 1973 20' SeaCraft. I moved the batteries to the front of the console with the Suzuki. It planed at about half throttle compared to FULL throttle with the merc. These boats are Very sensative to weight as you know.

Performance with alum props:
150 Merc Black Max 45 MPH
140 Suzuli 2 stroke 41 MPH (smooth and efficient)
150 Evinrude Intruder 52 MPH (hot rod bass boat motor)MY FAV
175 BRP JOHNSON 46MPH (Gas Hog, but otherwise good)

I know I'll run out of those light 60 degree Evinrude/Johnson motors someday...

I hope this helps, R&D (blown motors) cost a lot of $$$

Re: Repower could add too much weight?
 

Don't forget that these boats were made for STRAIGHT SIX Mercurys......about 275 lbs.