There are a bunch of MAF PCM friendly performance cams on the market and most all will work without a custom tune -- perhaps not perfectly but well enough if the cam is kept within reason.
Nearly all the major players in custom cams offer grinds to suit. Even old school cams like the Ford Racing E303 have been used successfully without a tune.
Initially, I think getting the 5.0 to breath better is more important than changing the cam. Mild porting of the heads and if using the original tubular exhaust manifolds, swapping to the later cast manifolds with a block off plug for the EGR would be a path to consider.
A different cam, or even simply moving to higher ratio rocker arms will also require better valve springs than original.
Still, for real gains, a more aggressive cam with matching valve springs, better breathing for the heads and exhaust with a custom tune are all going to have to be done. After that much better flowing heads become a path of necessity.
To paraphrase the old adage, "speed costs money, how fast can you afford to go?"
