Safe sucks! You should be OK with 245's and 275's. The front fender to inner fender bolts at the top of the wheel opening should be replaced with pan head allen bolts if the car is relatively low.....assuming front track width is stock. I'm running Kore3 hubs and IIRC they push the wheel out an 1/8" from OEM and I'm OK.
This photo will give you some idea of 4.75-5.5 and 245-275 clearances:
