I have 17x8" with 5" backspacing mounting 265/40s on my '67 convertible Firebird with just a little clearance, but I have a Moser 9" rear that's just a tad narrower than my original BOP 8.2. You could go 5.5" and slide a 9.5" back there. I've also seen 285/40s out back on birds.
I have 17x10 275/40 5.75 BS on my 67' I have drums now but discs in my future thats why I went with 5.75. Discs increase your BS by .25.
The front end is high do to no motor. The back is little high too, I will have to work on that