My 72 has M14 x 1.5 thread wheel studs (although it is 4 stud, not 5).

According to this website, you should have about 9.5 turns of the nut

https://www.drivenproducts.com/blogs/wheel-and-wheel-accessory-terminology/minimum-thread-engagement

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10