I dunno,might not be to hard...instead of grafting the letters of which would be difficult...what about taking a GT rear bumper and cut the lower part out and just graft the lower black cobra piece onto that,there wouldnt be a seam to fill in,I think if done right it would work.
Also maybe its just me but I think that cobra spoiler would flow better with the Bullit side scoops,I really dont much care for the bullit scoops but with that spoiler on there I think it would look better.