This issue is really coming to a head for me.  Also have a 1996 272 SF with original 2 strokes and re-powering is a matter of time. 
- 1996 Yamaha 200 2 strokes weigh 419 pounds each x 2 = 838
- I don't think the yamaha inline 4 200's will have enough mid-range torque so, for me, those are out. 
- New Mercury 225's weigh 475 pounds each x 2 = 950.  Total difference of 112 pounds. 
- New Yamaha 225's weigh 551 pounds each x 2 = 1102.  Total difference of 264 pounds. 
- Hondas and Suzuki's are even heavier . . .
With no more Evinrude, I'm a Yamaha guy and ideally that's what I want on the back of my Grady but at the end of the day I really think Merc's with only a 112 pound difference from original is the only easy option for new 4 strokes. 
That said, has anyone thought of, attempted or actually re-located the 3 batteries for this reason?  They have to weigh 35 pounds apiece, right?  Maybe more?  Say they are a total of 100 pounds.  If you could move them somewhere mid-ship you save 100 pounds on the stern.  (Place them on the bow and it's net negative 200, LOL 

  I was looking and I bet you could get two of them on the shelf atop of and behind the hydraulic steering reservoir behind the aft berth.  A third, I really don't know.  It would be an involved job for sure and I'm sure there are other issues I'm not aware of.  They weigh a lot though and moving them is something that just occurred to me today. 
Any thoughts?