454s on a 66

Capt,

a 4.25 bs 8" wheel will bolt on. You should run a narrower tire, and possibly need to roll the fender lips. It will look similar to taking a 4.75 wheel and using a 1/2" spacer widening your track width except it will have a deeper dish. Given all that, if you can find a tire that is 1" narrower than a 245/40-17 or 245/45-17, you could fit a 17x8 with 4.25 bs on a 66.

A 205/50-17 or narrower tire will tuck under a tight rolled fender lip. You might be able to fit wider if the fender lips are above the tire tread.
 
A 205/50-17 or narrower tire will tuck under a tight rolled fender lip.

Other than the whole stretching a tire onto a larger than recommended rim width range and all the curb rash that will give you from the lack of a sidewall and all the pot hole dings in the edges of the rim for the same reason...sure it bolts right on with that size ;).
 
Nick, I run a 205/40-17 on a 17x8 with 4.75bs on my daily driver 63 wagon without any curb rash. A 205/50-17 tire has 7.8+/- tread width depending on what brand.
I suppose on a 66 with the 4.25 454s with the front control arms brought all the way inward and a vario-centric camber kit bringing the lower control arms inward, this could help if you want a wider tire and tucked.

Or, try an alternative wheel. These guys will custom your wheel bs from 3.75-5.25 on a 17x8.
Team III Wheels [AC III Wheels]
 
Nick, I run a 205/40-17 on a 17x8 with 4.75bs on my daily driver 63 wagon without any curb rash. A 205/50-17 tire has 7.8+/- tread width depending on what brand.
I suppose on a 66 with the 4.25 454s with the front control arms brought all the way inward and a vario-centric camber kit bringing the lower control arms inward, this could help if you want a wider tire and tucked.

Or, try an alternative wheel. These guys will custom your wheel bs from 3.75-5.25 on a 17x8.
Team III Wheels [AC III Wheels]

Yeah but there's no potholes in Ohio and you don't parallel park it :p

You're still shrinking the sidewall and installing the tire on a rim not recommended by the manufacture. I'm sure it is done all the time without issue but you do increase exposure to damage to the rim. Did you buy the tires and then take the tire and the rim to shop to mount them?
 
There are a lot of wheels that look very similar to the 454s. Get wheels that have the right BS and width for your application.

The section width on a 205/40/17 tire is wider than the tread width, about 8.3" but a 17x8 wheel is 9" wide. That's about 3/8" of exposed metal that will quickly develop rash. Looks ricey in my opinion too.