Depends on your goals, spare cash, and availability.
If you really are going to quit at 300whp, stock parts should suffice quite nicely. If you get the bug and end up with a 500+ whp monster, you'll be bitter that you didn't replace a whole lot more of the internals while you had it apart the first time...
Seriously tho, the headgasket is the only serious deficiency in the 7M. Fix that and you're set.