1964 stepside wheel question

[Pvas580]

So I recently purchased a 1964 Stepside with original wheels 15x5.5 and was looking to go a little larger. Purchased some rally wheels 15x8 with the 9 slots. Believe from a 4x4 circa 70's or 80's. Did a test fit and they seem to wide. The rim lip looks to be just inside the fender lip with little clearance. I have not mount tires yet and wondering if I should look for a more narrow rim? Maybe the same wheel in 15x7 that Chevy used. These are 6 lug and my plans are to use till I swap to 5 lug in a year or two. Thanks for any help.