Once you have removed the heads - the difficult thing is knowing when to stop! e.g. if you replace the cam/sprockets/lifters what about rockers, pedistals and shafts? rings, bearings etc, etc.

for info - I recently removed the heads from 3.5EFI after discovering it had a split exhaust valve, and had the heads completely reconditioned - new valves etc, etc. Cost $1k and about 13hours of my time. And it only made a very marginal improvement - so I think rangieman's advice is pretty sound!