It's possible but a lot of work.
Look at my engine build. I have 232WHP with stock S52 cams, overbore, and 11.5:1 pistons. Runs on pump gas.
With an agressive cam (sunbelt/evosport) and some head work I could probably up that number by 30-40HP, but even then, I'm still relatively far from your "300WHP" mark.
Now if all you care about is bragging rights, then you can easily say that my engine has 275HP (at the crank), and therefore with the cams would have well over 300hp.
Now, I spent about $5k on the motor (complete rebuild incl. bolts, guides, bearings, pistons, machining, all new sensors as well as bolt ons like pulleys, intake, headers, custom exhaust, and cams). If you wanted to go with an aggressive cam, then you're looking at about another $3k for top end work...
So for less than $10k you can have a "300+HP" N/A M52 that will be fairly reliable, and insane to drive on the street.
Last edited by sb_600; 10-19-2012 at 12:48 PM.