Merc XR2 thoughts opinions?

[McGillicuddy]

Looking at a late '80s Merc 150 xr2 25" for under $1800.
Any thoughts on this motor for my '72 Seafari. They are a little heavy at 378 lbs or so but I think it may be more economical to run than my 115 I-6. Any thoughts on this, Bigshrimpin? Fr. Frank? merc gurus? What block does it use and what might I get for fuel economy assuming the motor is clean? I'm currently cruising 25mph @ 3700-4000 rpm getting 2.5 mpg with a 13-3/4x 15 aluminum black max prop. Really poor economy at trolling speeds (maybe 1.3mpg) Somedays we're getting YFT and BFT within 15 miles of the beach but more often we're running at least 40 mi. each way. Sure would be nice to increase my range.