If a mini-spare is preferable, you should be able to get one out of wrecked Focus right back to the early 2000s, most of them had a 15" mini-spare that will clear the larger brakes on the 08-11 cars.
"M" engine code in the VIN was used on 86 5.0L HO Mustangs, and also the Mark VII LSC through mid 87, when they still had the py E6SE swirl chamber heads, basically the 200 hp version of the HO, not the 87-up Mustang 225 hp version. "E" was the VIN code on 87-up 5.0L Mustangs and the later LSCs that got the better heads and matching pistons.
I tried scrolling back through several pages of your previous posts, but didn't see anything. Can you share with a newbie to this forum some details on your car? Do you have a build page on it somewhere maybe?
If you're looking for something to use year round, don't go much wider than stock ... think snowshoes vs. skis. Continental Extreme Contact DWS, and the updated version DWS 06, are probably the best performance all-season tires for snow traction. They are available in 225/55R16 and 225/50R17. I definitely would NOT suggest going with a 245 or 255 width tire unless you are going to run different tires for winter.
That would actually be my suggestion, put whatever you want on for 3 seasons of driving, and then get some dedicated winter tires that fit your stock wheels. Firestone still offers their Winterforce in 205/75R14, which would be perfect. They are a bit noisy on dry pavement, but other than that are good performers.
My father had an 80 Bird brand new with the awful 255 V8. What a letdown of a car after his nice 78 T-Bird. He was a salesman and usually swapped cars out every 2-3 years. Prior to the 78 Bird he'd had a 75 Gran Torino and a 72 LTD. After the 80 Bird, he didn't get another Ford until 1990. LOL
The Crown Vic wheels would be too low on the offset to use on a 5-lug swapped Fox Bird, but the version that was used on the 90-92 Mark VII LSC would be just about right. And I agree, the classic mesh wheel would look great on our cars.
I had an 85 Marquis LTS (the Canadian only Merc version of the LTD LX) back in the early 90s as a daily driver. Fun car, nobody had any idea it was anything special.