I put ridler 18x8 with 4.50 backspacing. Has 1968 12 bolt rear and is supposed to be same width as a 67 10 bolt buick. Fender lips have been trimmed to accommodate a 235 wide tire. Note that there is 2 plus inches of clearance between frame and tire so could definitely use more backspace
They should be fine front and rear, depending on tire width. I use 17x8's with 4.5" backspacing on my 64 and they're fine with a 225 tire's up front and 255 tires in the rear and that is with disc brakes up front. Drum brakes will give you more fender clearance. I tried an 8" wide wheel with 5" of backspacing up front and rubbed the sway bar at full lock.