We went through the same thing with an EJ wagon that had been in the family for nearly 40 years. It was registered in the 70's with a 149 in it and we let the rego lapse in the 90's. Went to get it registered again in 2012 and they wanted a full engineers certificate for the engine swap as a Red 6 was not an option on the EJ. End result was sourcing a Grey 6 to put in it and registering it that way.