The 3.0L merc's are PIGS. I'd go with the 150's . . . they're lighter and much better on fuel. Make sure you check compression on the motors and run them (if possible). If you find that you need more HP . . . there are bolt on mods that can be done for little money on those 150's.
www.screamandfly.com byuboyz.com have lots of good info!!