I agree with them. There are other differences such as the exsillary (sorry about the spelling) shaft is longer with a gear to drive the dizzy out of the timing chain cover, the oil pump in the 18rg is a high volumn compared to the 18rc, the pickup in the sump is different, as well as the baffels, then you will need to get carbies and manifold, or EFI and exhaust, as well as some chain guides. If you had done this before it would be to bad!?! I'd buy a complete 18RG. Good luck.