Jay Mays claims most of the influence was from the 66-68 models, and that's visible in the nose and fastback, but there was also some 69-70s influence. The 68 and earlier fastback had a nice fastback, but I like the 69+ Larry Shinoda Boss Mustangs a lot also, perhaps more than the first Mustangs.
I actually think the Mays design may surpass any of them. Though of course it draws strongly on them, it is very clean and modern yet at the same time forceful, and almost a little Teutonic in the pure lines. The hood proportions aside from the actual nose looks almost BMW 3 series of a couple generations ago. But what really gets my attention is the clean side profile. Straight and simple yet strong, like classic middle America.
Ford should have a winner in the new Mustang. The LS platform the show car is based on is good, if somewhat heavy. It underpins Jags, Lincolns, etc. Certainly it's lightyears ahead of the old 1970s Fox platform that today's Mustang is still based on. Ford hints that in actual production, the new Mustang may have a simpler platform than the LS however, with a cheaper and simpler live rear axle and front struts, rather than the control arm front and independent rear of the LS. That should keep costs and weight down somewhat, though at the expense of suspension sophistication.