you could piece together and 03 longblock for fairly cheap. probably 5-6k.
instead of spending the 500 or so getting a heaton for it, i would just go straight to a KB/Whipple though and do injectors, bap, maf, ect all at once.
if your not going to take advantage of the 03 shortblock strength, then id just built a boosted 331/347 instead. easier and in the end same or less money for the power.
check out www.Modularfords.com it has alot of info on Mod swaps at one point I wanted to do a 96-98 DOHC cobra motor in my 93 all in all it's not too much work but there are plenty of writeups you can check out. I bieleve ford sells the motor for 12k dont quote me but it's somewhere in that range. I have also seen complete 03 cobras wrecked going for that which would be a better bet so you can get all the accesories, hydroboost, electrical etc. Good luck