I do not know how much time and effort you want to put in to convert the Scalextric Gulf GT40 to another version? Firstly let me say I am not trying to put you off! Since the Scalextrics is inaccurate anyway. The nearest version to convert too would be a late Paul Hawkins car since the rear deck would have too be modified to fit wider wheels and tires. The sides of the deck would come down square. Also there would be a bulge on the lid for the spare wheel. The colour would be Red. A lot of work would be needed. I think a more unusual colour scheme would be that of chassis P1080 in John Allens super profile book page 55. In its penultimate race at Vila do Conde in 1979 it looks as though it was in white with a band of two shades of blue and one of black applied going along the sides and accross the front and rear body work. The shade of Blue is also applied to the six spoke BRM wheels. Although you will have to replace the Scalextric version with the Flys to get a better and more accurate wheels. Since at the moment I cannot post pictures. If anyone could post a picture as described you would be able to judge for yourself. The only other car that might be OK with the kit is the number 11 Gulf Lemans car P1076 Brian Muir/ Jacky Oliver at the 1968 race. One, it was the only Gulf car to run with a spoiler. Two, it had a normal door handle (the two others had quick release handle). Three, the Marigold stripe down its centre was widened on the front lid coming down to a point at the front with a Cibie sticker over it. The only thing that needs changing is the rear deck vent which is not the 9 hole one on the Scalextric but a 'normal' version. This car lasted for one hour Muir ramming it into the sand bank. See if you can go onto the Lemans Miniatures website (lemansminiatures.com) they made a 1/24 version some time ago. Good luck!
Regards Allan