You will have to do some fender rolling and possibly run aggressive neg. camber settings to get 7" wheels to fit, but they will fit.
AFAIK 8" will not fit your early nonflared car. A great street setup for the early car is 6x16 Fuchs, which are readily available at decent prices because they were used on the front of the 911 for many years. The selection of hi-perf tires is MUCH better for 16" wheels than for 15" too.
Chris C.