Mike, I think the oem wheels where 5", and 3" backspace. Long time since I measured them and I wouldn't trust my memory completely.
My bird runs 15x7 front, 3 1/2 inch backspacing. 225/60 15 T/A's. Some guys say you can go 4" on the front, but mine are as close as I'd go from the sidewall to the upper ball joint. 4" wouldn't clear on my car.
The rears are 15x7 4" backspace with 235/60 15 T/A's. No skirts, and very tight to the outer fender lip.
I wouldn't have gone to those sizes, but the local tire shop did the measurements and guaranteed they'd fit. It was damn close, on a left hand turn the left rear would shave rubber. The body was 1/4" off the center of the axle, and relocating the body just solved the problem.
If I were doing it over, I'd be 15x6, 3 1/2" backspace, and no more than a 225, probably a 215. Aspect of 70 or 75. The 60's work for me because the car is lowered and they fill the wheel openings.
I know this doesn't help a lot with a Parklane, but the front suspension is the same. Some have reported with larger wheels and tires they need to drop the rear shocks off to change a tire.
Years ago Wheelsmith made me a set of 15x7" rims on factory 55 centers. They used the factory dog dish, and put 10" cheater slicks under the back of the bird. Looked great sitting, driving on those not so good. They might be worth a phone call.
https://thewheelsmith.net/
miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ