Blue, I don't know much, if anything about jack plates ( ain't they a southern thing - where you at anyway?). Won't a jackplate, by raising your motor 5 inches, put more of a torque strain on your transom? Kind of a lever effect. Not such a good thing, especially in your case.

I don't think a carbed 140 hp would be inadequate for your v20, might even be a good idea to take it easy on the old girl. I just think they are crummy motors to begin with, and the ones you have -- let's just say -- I don't see much of a future for them. Face it -- a pair of 15 year old, 25 inch shaft, counterrotating 140's. As Airslot indicated above, you need less length on twins because you are outside the bottom of the V. That tells you that they were pushin a big boat. Sell them, and buy the best 20 inch shaft 150hpyour money will buy - that is what I would do anyway. :)