The tire size of choice is 235/60 15 (front) and 295/50 15 (rear).
I can't speak for SVM but I can only suspect that the reason they say "suggested" is because tire size, just as engine size, is not cut in stone. I have seen guys use 17" low profile (read expensive) tires. Truthfully, the tire size I used looks good and lends itself well to the era in which the car originates. I'm using Dunlop GT Qualifiers. Personally I think they look better than low profile.
Sorry to hear you're having a hard time. Building a kit should be a fun project and I know it's a bummer when things don't work out. I'm not patronizing you. I know from experience in building kit airplanes. We used to sometimes subcatagorize kits as "builders kits" and some as "straight kits". The builders variety required more effort and time. I guess in some ways, the SVM leans in that direction based on the required welding and fabrication of some components.
My only advice is to be patient and take every step with careful planning. If you have any questions, please do not hesitate to email at my home and I will help you out the best I can.
Campy
pcampjax@telocity.com