Actually, it's not that simple, given all the variables.
And given that you're going to be spending at least $1,200 - $1,500 on wheels; $400 - $800 on tires. We should get this one right the first time.
What backspacing does SV recommend, F, R, using what size wheels and tires? Do you intend to use this size wheels and tires?
Does SV offer a "Factory" wheel? What is its' size and backspacing?
What front suspension are you using? MII stock? MII aftermarket tubular w/coil overs? What front brakes are you using?
What differential are you using? '80's and early '90's Mustang 8.8's are one width. From about '95 up, they get wider requiring more backspacing. Other FoMoCo 8.8's off Continentals are wider requiring more backspacing.
Case in point. I have a Classic Roadsters (CR), not an SV. But they are similar.
Plus sizing to a larger tire/wheel. Some like the originality of a 15" wheel/tire. And with due respect, 15" wheels/tires were the performance tires of the mid '60's and '70's. Grocery getters were running mostly 14" tires, and some econo-boxes 13"ers. That was then. Today, the performance tires are at least 17", requiring a 17" wheel. Going from a 235/60R15 to a 235/45ZR17 tire will give you a tire that is the same diameter (roughly 25"), and a narrower sidewall because there is no sidewall bulge. Tires are less likely to rub the fenderwells at the sidewall bulge. Backspacing should only change if you go to a (substantially) wider tire and wheel.
My CR front is aftermarket MII with 11" brakes. Factory (CR, not Ford) wheels were Cragar 15" x 8" w/4" backspacing. Factory tires were 235/60R15. I plus sized to 17" wheels and tires. Wheels were 17" x 8", tires were 235/45ZR17. Backspacing remained the same at 4".
Rear is '84 Mustang 8.8. Brakes are SVO Mustang rear disk brake conversion kit which uses T-Bird Turbo Coupe 10" rotors. No dimensional changes from original drum brakes. (But some disk brake conversions do have dimensional changes, in, or out.) Factory (CR, not Ford) wheels were same as front; 15" x 8" Cragars with 4" backspacing. Tires were 255/60R15's.
I plus sized, and plus width'd to 275/40ZR17 tires, and used a 17" x 9 1/2" wide wheel. Ideally, the backspacing should put the wheel centerline directly on the the wheel mounting flange centerline, or 1/2 wheel width. I measured the tire to inner fenderwell clearance, and outer fenderwel clearance and found them about the same. My ideal backspacing should be 1/2 wheel width, or 4 3/4". But if my eyeball calibration is off and additional clearance was needed, would it be easier to shim the wheel out a smidgen, or in a smidgen. I ordered my rear wheels with a 5" backspacing thinking I could shim the wheel out a smidgen if necessary. It wasn't necessary. Everything fits, and everything works.
Ride height. Assuming your front and rear ride height can be adjusted, here's what I've found to be the determining criteria.
First, find out what the lowest point between your car and the ground is. This will likely be the "Chin" portion of the frame, the
oil pan, the bellhousing, or the trans. The softer your front shocks and springs are, the greater this distance should be. 5" - 6" should be the absolute minimum for street ground clearance. And this will determine your front ride height.
Rear ride height is a little more flexible because car parts should not be in danger of scraping the pavement due to speed bumps. Once front ride height has been set, look at the rear. You want the top of the rear tires, and the bottom of the rear fenderwell to be apart by 1" - 2". If you have to do a lot of adjusting at the rear, you might have to readjust your front.
Now roadtest it. No rubbing anyplace? Now go to an alignment shop and have the front end alignment dialed in. Yeah, they look at you and say, "We don't do those here!" Be persistant, explaining that the front end is a '76 - '78 MII. This the front end shop has alignment spec's for.