you can install a older motor BUT ONLY if you run it on LPG thats the rules so it runs cleaner emmisions
id stay away from a 18rg anyway you have to fab new mounts up and source a front sump from a corona, easier to install a newer motor and run on regular unleaded as johnny howard is taking the fuel tax exemption of LPG in a few years anyway so it wont be as cheap as it is now, for much longer