twin vs single outboard

[usmma2013]

Hey guys,
My v20 came with a 140 evinrude bubbleback that needs a rebuild(Scored piston). I have a extra powerhead already bored 030 over and I was going to hone and deglaze the cylinders and give it new rings. I have all the parts and was going to rebuild it and put it back on..before a craigslist ad caught my eye for 2 85hp Mercury i4 outboards, both running, for 600$. While I love the thought of having twins, I THINK that...
a) I'm not sure the transom would appreciate the extra weight
b) Fuel economy would probably be much worse than with a single 140 or 150.

Trying to talk myself out of the idea before I end up with more un-used outboards sitting in the garage..

thoughts?
thanks
MJK