As great as Mike Psiaki's 10248 Creator Expert F40 set is, it definitely benefits from extending the wheelbase and rear end by a stud to improve the overall proportions. I made this modification back in February, but I was recently asked for the parts needed to make this change and have subsequently spent the last few days building the modified version in LDraw so that I would have a permanent record of the mod to use as instructions. And now that it's done I might as well share it here for anyone else interested in making the same adjustment. I've also removed the stickers and windscreen printing, and replaced the printed C-pillar wedges with plain red ones. The extra stud of length is added to the doors, side skirts, and space between the rear window and wing.
LDraw File: [FREE DOWNLOAD]
List of needed extra parts: [FREE DOWNLOAD]
Extra Needed Parts