ARP don't make 18RG studs, and I'm not certain of the compatibility with 22R studs. I will be checking this soonish though. If the 22r studs did fit, there is also no guarantee the 22r bolts would fit...
If you want a set of really good 18rg head studs, there is a group buy happening at the moment. (If you are certain they are interchangable with 2TG ones that is...). They are $200 a set. PM yellorolla if you are interested.