Question for those running 17" Mustang Bullitt wheels - spacers
In the front you need to use a spacer that will fit over the hub. Typically the spacers made for the newer Ford Mustang's have a 70.5mm hub bore, the Mopar hub for the 73+ disks is more like 71mm. Although it does depend on who made your rotors, the hubs can vary a little because they aren't always finished the same. Usually they're on the larger side of 71mm if they're different. It isn't much, but like the wheels the spacers need to be opened up a bit, or the hubs turned down a little. The Mopar hubs also protrude out more, so, even though the wheels may work at the mounting surface a lot of the wheels will have hub bores that taper down to a smaller wheel cap. That doesn't usually work, the mopar hubs will stick out past the wheel with a lot of wheel designs, so you have to machine the hub bore to be uniform all the way through. That's what I had to do to my Enkei RPF1's. They start at 73.1mm at the mounting surface, but taper down to a like a 2.5" cap which doesn't work well with my 2.7" diameter hubs (Dr. Diff 13" brake kit).
Pauly has it right on the wheel clearance, the issue is the tie rod in the front, not the caliper. The Bullit rims specifically run out of clearance to the tie rod end at about 5.6" of backspace, so you need about a 1/8" spacer with the 17x8's with 5.7" of backspace. Not all rims run out of clearance at 5.6", the Cobra R 5 spokes from similar year Mustangs can run almost 6" of backspace, has to do with the design and shape of the lip on the rim. The OE Bullit's are pretty well documented to need 5.6" of backspace, and that takes a spacer.
In the back you don't need to open anything up for the hub bore, the spacer takes care of it. The link I posed above goes to a set of 1" spacers than are 5x4.5" to 5x4.5", although they make them in adaptors that change pattern as well. These are them.
In the front you need to use a spacer that will fit over the hub. Typically the spacers made for the newer Ford Mustang's have a 70.5mm hub bore, the Mopar hub for the 73+ disks is more like 71mm. Although it does depend on who made your rotors, the hubs can vary a little because they aren't always finished the same. Usually they're on the larger side of 71mm if they're different. It isn't much, but like the wheels the spacers need to be opened up a bit, or the hubs turned down a little. The Mopar hubs also protrude out more, so, even though the wheels may work at the mounting surface a lot of the wheels will have hub bores that taper down to a smaller wheel cap. That doesn't usually work, the mopar hubs will stick out past the wheel with a lot of wheel designs, so you have to machine the hub bore to be uniform all the way through. That's what I had to do to my Enkei RPF1's. They start at 73.1mm at the mounting surface, but taper down to a like a 2.5" cap which doesn't work well with my 2.7" diameter hubs (Dr. Diff 13" brake kit).
Pauly has it right on the wheel clearance, the issue is the tie rod in the front, not the caliper. The Bullit rims specifically run out of clearance to the tie rod end at about 5.6" of backspace, so you need about a 1/8" spacer with the 17x8's with 5.7" of backspace. Not all rims run out of clearance at 5.6", the Cobra R 5 spokes from similar year Mustangs can run almost 6" of backspace, has to do with the design and shape of the lip on the rim. The OE Bullit's are pretty well documented to need 5.6" of backspace, and that takes a spacer.
In the back you don't need to open anything up for the hub bore, the spacer takes care of it. The link I posed above goes to a set of 1" spacers than are 5x4.5" to 5x4.5", although they make them in adaptors that change pattern as well. These are them.