There is a link in the FAQ section that deals with Rally Codes. I purchased a mix set of JCs and HKs and the only difference I could see is that the center section (where the cap goes) was a little narrower on the HKs. Once the cap is installed you can't see the difference. I could not see any functional difference but being a purest, I opted to go with JCs all the way around. I don't believe the HKs were ever used on the 1st gens.

BTW, the HKs I bought were trash and I ended up scrapping them. Don't get burned like I did. Make sure the beads and the lug holes are in good shape before purchasing.