US Indy slots...man I love these wheels...

I have been running the ETII slots since the 70s. My favorites, too. Currently running 5x4, 14x7s on front, maybe 3.5b.s.? on my 68 S-clone.
If you try to run too much b.s. on these early As the rim will hit the upper BJ. A 15 is better, but you still run out of room in a hurry. A ran a 15x8 inch Wheel Vintiques Rallaye wheel for a summer a few years ago. I think it was a 4 inch b.s. I had to do some "clearancing". The tire wanted to hit the inner fender/frame at the rear as well, at full lock.That was a steel wheel. Aluminum would not have worked.
With the 8 wide, and a 245/50-15 rubber, I also had to trim the fender for turning clearance.The bottom front corner. A little wedge, about 1 inch at the bottom ,tapering to 0 about 3 inches up.
I recommend you jack your car up and measure ,very,very carefully.