Well, the short answer is yes. A 275/40-20 and 315/35-20 tire combination will fit, but it will be really tight, especially on a lowered car. I would not recommend the 40-series tire for the front, although I've heard some people are doing it. For the front, I would run 275/35-20, which many tire companies make.

Saleen runs a 275/40-20 on the rear of many of their Mustangs and that tire is about 28.66" tall. Your 315/35-20 is similar, standing at about 28.68" tall. The issue is the width, which I imagine will require some precise measuring and a custom offset wheel. I think you'll need to roll the fender as well, especially on a lowered car. The better option would be a 295 or 305 width tire.

Any time you change the overall tire diameter, you will need to re-calibrate the speedo or the check engine light / dash alert will trigger. Any aftermarket, handheld tuner can do this (SCT, Diablosport, Granatelli).