Be careful with the 18RG. Some rego inspectors let it go, while others can be a real pain. Problem is the emmision. If you get the EGR valve (I think it's call that) hooked up it should be o'kay. I've got a 18RG in mine and it goes through rego. Also if you want some more power look at some cams, valve springs and rejetting the carbies. With largish cams (292 duration or 238 AT .050") AND 430" LIFT it pushes the Ra40 along nicely (approx 160-170hp), but mine has also been ported and balanced and has extractors . Good luck