I might be missing something, but why make life difficult? If you want a dedicated attack platform why not just admit they got it right with the Skyraider. Start with that, upgrade the avionics, put a DAS on it and don't muck it about so much you end up with a flabby mere rather than a thoroughbred.
Surely they learnt that post Korea when they unsuccessfully tried to use P-51s in the attack role having phased out the P-47?
I would also suggest that 'Attack' aviation is subtley different in ethos and mindset as well as capability. You can't just put a cannon and a PW on a FJ used to operating at 20,000ft+ and get the same results. It's about the whole package, they'd do well to remember that whatever they pick.