i have put headers, throttle body spacer, k&n cold air intake, msd ignition coil, have to keep emeissions friendly, but still seems like it has a lot more power that can be unleased. is there any suggestions on what else to upgrade without getting deep into the block itself?
Horsepower costs $$$, how fast can you afford to go ?
This stuff is all pretty basic. You've already got the headers so that's good, next on the list should be an intake, cam. After that you'll want a larger throttle body & a new chip (the larger TB makes no sense until you can *use* the additional fuel and the chip will get the processor to work with all the additional air you're moving thru the engine). Once you've done all that if you still want more then you need to either have your existing heads ported or (really the better choice) buy a set of new aluminum heads that already have larger valves, better porting and higher flow numbers. If you do all of THAT ans you're still wanting more then a blower(supercharger) is probably going to be what you want. The new breed of centrifugal superchargers work well with the 5.0's and a stock bottom end is strong enough as-is provided the boost is kept sane.
Of course you have to look at what you have & where you want to go, sometimes it's just a whole lot cheaper and easier to swap in a larger engine. The 351W and 460 are bolt in upgrades that provide a lot more HP & *torque* than anyone will ever see from a 5.0 but a well built 302 is an excellent Bronco engine (especially in the 66-77's and 80-96's, not so good for the heavy 78/79's)
I'd stay far, far away from nitrous. You need additional electronics to manage both the spark & fuel when using it and even with that it's still way too easy to cook your block. Also, on an unrelated note the penalty in this forum is quite severe for using the word "noss" (which isn't even a damn word anyways which just goes to point out the basic level of education of those who DO use the term) so just don't. Stay away from the stuff.
So there you have it. That's the roadmap I'D use anyways.