Rod,
My reasearch has shown that there are indeed differences in the rear clamshell on GT40's...that includes the origionals as well. If you look at pictures in the gallery, you will notice that the origional "narrow tail-twin tailight" version is different than the later single light version. Also note the rear wheel wells, some of them have a round contour and some of them are eliptical...more oval in shape and cover the top of the tire more in side profile. Very confusing since I have seen two origionals..P1043 &P1046...both narrow-tail twin-lights..and they have different wheel well openings, however the rest of the clamshell appears identical to the eye.
The early single light narrow tail bodies are almost the same as the twin-light versions, but changes show up later. By the way, RCR has the most perfect narrow-tail single tail light version in the market to my eye, but that is because they have an eliptical wheel opening which looks more origional to me...however, that's just my opinion. SPF does a great version of the MKII, very accurate and virtually identical to Holman Moody's MKII which is produced from their origional molds and diagrams form 1966.
In short, you will have to decide which look floats your boat and make come decisions. IMHO, that is the hard part. Do you want to replicate the MKI Road Coupe, Sports Coupe (street version), one of the racers such as the Gulf cars (wider rear body work..eliptical rear wheel weels, single nostril) or one of the MKII versions. Choices, choices! Keep in mind that there were only a small number of cars ever produced and running changes were occuring all of the time..trying to improve their winning percentage.
I am going thru the same decisions as to which manufactuer is the wayto go for me. I also have the problem of size sice I am 6'2" and 230lbs. You too will have to decide how you want to use your car and what fits you and your significant other's idea of fun.
Garry