Eh, the LS1 is great but it's just an aluminum small block with factory heads/intake that flow well and a decent cam.
Strip a LS1 and a 351W down to shortblocks and then build them back up with the same amount of money and they'll be pretty much even. I think if Ford had a fuelie 351 option for stang(besides the R obviously) it would be just as good as the LS1 in terms of mod potential. As it stands we have to rip 351 rollers out of trucks and swap them into stangs and jump through all kinds of hoops vs just bolting on a HCI like the Chebby guys do with the LS1.