Mochaman,
You will have to measure to get the answer. It all depends on how low (or high) the stance is. If very low, say in the rear, you will have to first find total distance from the quarter panel lip to the first place inboard that the mounted tire would hit. That would be the front portion of the inner wheel house. That will roughly be the distance to the leaf spring, on cars with leaf springs, because you will have to hammer that area for clearance.
Measure from the front surface of the disc (or drum) hub back to the leaf, or calculate where the leaf would be, with coilovers. Then measure from the hub outward, with a plumb bob hanging from the inside of the lip. The total will be 10"-10.5" on '65-'66 Mustangs and Falcons.
Draw it out on paper, and figure the backspacing and wheel width required to be centered within that space. Then add the OAW of the tire you want to use, allowing for clearance to the inside and outside. There's a great tool for simulating all that at the "Tools" option "Size comparer" at rimsntires.com. It will show tread width, OAW and diameter of any size tire. Choose the rim diameter, width and backspacing. Keep in mind that an 8" wheel is actually 9" wide at the outside, lip to lip.
The sidewall width is more important than tread width because that's what has to "fit" in the wheel well.
235/45s are 9.3" wide, 245/45s are 9.6". Some have fit 245s on the rear, but there is variation on these cars, from the factory.
If you go very low in the rear, the "eyebrow" arch above the lip is the point of contact when the suspension is compressed.
Obviously, the dimentions are less critical for a stock height suspension.
Measure out the front in the same way, and account also for tire clearance at full turn.
You may have to roll the lips to get the look you want.
 

Thanks Steve and Whlnut.
I too have the Versailles rear end. I have original disc brakes but plan on upgrading after a while. Push now is to get car on road for next year.

The 01 tires rubbed on the inside wheel tub which led me to really look at the dish depth. Plus they looked wierd sitting so far inside the fender lip. I am thinking about doing the 8" in back and 7" up front. The Fatman front end had lost of room on the inside of tire.

My original wheels and tires that came with car. 215/ 60R15

I think you should install the engine, and at least the equivalent weight of the other stuff before you decide on wheel/tire sizes. You will have to determine final ride height, then measure for the right clearance. I spent a LOT of time on my choices before ordering exactly what I needed.

MustangSteve wrote:

Same size 17x8 wheels.  I have Versailles rear which is wider.  Rears do not rub.  Don't forget that when cornering, the rear axle leans to the side which will make the tires rub inside the fender.  You have to leave more room than you would think.  Fronts are same wheel, just narrowed to 7" wide (so now have backspacing 4.72")

I measured rear ride height the other day and it is 13.5". Front is less, but I may lift it up about 3/4" from where it is now.

Where is the 13.5" measured from?  what is the wheel backspace?  Are the front or rear fender lips rolled?  What tire size?  Are your front a-arms relocated down?  What front springs are you running?
Thanks.

Thanks again.

cool beans paint code and manufacturer would be great.