you can remove the heads and the cam and lifters with the motor still in the bronco, if you have a lift i guess you could remove the crank and pistons but it would be a lot of trouble. I removed my oilpan on my 460 on a lift and seemed to have enough room to take the crank out but it would be tough and i'd be afraid i'd drop the crank and then have a broken or scratched crank.
for more performance, i'd put a 4bbl intake and a 4bbl carb (holly or edelbrock) and then put a cam and lifters in (don't just change the cam, change both at same time), could also put a better ignition system on it to give it a higher spark and create more hp.
if it was me, i'd pull the motor out if possible because it makes it so much easier to work on. Don't have to worry about getting in and out of the bronco to get a tool just to loosen one bolt.
hope this helps
definetly just recommend pulling the engine and doing a proper rebuild. If there is any emmisions crap on your rig at all remove anything not vital to engine operation including all vacuum not needed.
But you can take your heads off easily and either replace them with some aussie heads or just rebuild those. You can bolt on some headers. Of course cam change, intake and carb. Good dual exhaust with some free flowing mufflers. Trying to pull the crank while the engine is still installed is a waste of time, might want to pull the pan to check out a few bearings and seals but that's about it.