Re: 153 stroker?
Why not look for a rebuildable 140? Your going to need the entire rotating assembly (crank, pistons, rods) out of the 140 anyway and it would make more sense to punch a 140 block to .030 over than to hog out a 120 to 4.000 to put in stock 140 pistons (if it can be bored that much), then buy a $2-300 140 crank kit (2.00 or 2.10 rod journals?), and the source rods. I'm rebuilding a 140 right now and the rotating assembly looks to be balanced by Mercruiser since the crank has lots of grinding marks on it, replacing the pistons shouldn't affect the balance that much, but if your piecing an engine together you need to have it balanced for optimal performance, another $150-200.
At a minimum I would look at building a 140 shortblock and use your massaged 120 head and manifold (I'm pretty sure the 120 head and manifold are different than the 140). Heck, after you do all that expensive machine work and buy expensive 140 internals, you going to end up with a ,,,,, 140, makes sense to start with a 140 from the beginning.
What ever you do, look at building maximum torque, that's where it counts in a boat engine.
