Stay with the Volvo, the switch to Merc is costly. The Alpha is weak compared to the Volvo, the Bravo is far more durable but will cost you 2-3mph at top end due gear case size. Since you have already considered redoing the transom for a Merc setup think about raising the X for your setup. You can get decent performance out of the Volvo with a nose cone and even more important raising the X, only a few of the knowledgeable have raised the X on Volvo setup.
No matter what your beliefs are "GOD BLESS AMERICA"
Fully retired marine tech near 60 years in the biz.