New to Racing Junk forum. Anyhow, a little late on BobOs '81 Mustang. I actually work for a company manufactures and builds drag race wheels. We build a Sportsman series drag race wheel in 15x3.5 through 15x15 aluminum in 4 lug and 5 lug.
www.spinwerkes.com, or (562)467-1522, there's a picture of both those sizes on the website. The website is very limited on access.