[TheTinMan]

Stinky, for your 18 I'd consider the small block 140, less weight than the 150 big block.

edit: just checked weights:

140 small block: 420 lbs.
150 big block: 474 lbs.

Both 25 inch shafts

There's probably more than a 10 hp difference too. The 140 is said to be a little overated, probably closer to the low 130's hp.