Yes they are 7.5”. I am not worried about it 1 since I don’t air way down and I don’t worry about popping the bead off, 2 even Firestone says 7.5” is the narrowest wheel and 3 I may go with a weld on bead lock and won’t ever have to worry about it.
I would run a 7.5” with 315’s.
The FJ Cruiser wheel is narrower than stock and has more backspace than stock. The net result is you have narrowed your track by by almost 1 3/4 inches. The references I find list a minimum rim width for this tire to be 8.5 inches. You will be fitting a tire with a 10.2 inch tread width on a wheel with a flange-to-flange width of 8.5 inches. You will have quite a crown in that tread unless you really drop the air pressure. Your call.