I too just want to add a 3 minute version of woe tale when dealing with the RTA.
This thing of mine "Hellspawn", a series three converted to 186 from four cylinder, was modified back in the early 80's when engineer's reports weren't much hack. The engineer did all the work and an RTA inspector would actually approve the modification. Where as nowadays it's the engineer who gives the nod and the RTA make things more difficult for an engineer to approve modified vehicles.
Now this is how thick the RTA is. When mine was modified it was approved to 186. Then that motor wore out so an exchange of same capacity was put in (179 rebored out to 186) and id number changed. That motor snapped no. 5 conrod not long after I bought the vehicle of the owner who modified it all those years back. I replaced the 179 block with a similar 186 to the original.
When I went to change the record with the RTA, they would not recognise that the vehicle had been bought back to it's original approval configuration, ie a 186 engine and bantered about the scrub I have increased the performance of the vehicle going on engine numbers alone. Hello ! So I got the original approval certificate out of them and showed that plus my rego plus the old block. They still claimed performance enhanced and wanted an engineers certificate before they would 'adjust the records'.
I spoke to an engineer (showing the same things I did the RTA) who politely agreed with them so as to get my money and informed me that the engineers certificate lasts only 10yrs so as to prepare me for this idiocy again or keep himself in business.
Loop hole ! I got a safety certificate, registered as was previously and still trot around in a vehicle that has the performance in the RTA's view of a 350 chev in a moke. Every year I produce that original approval certifiacte and no questions are asked regarding numbers. Why ? Saftey certificates don't worry about engine numbers.
What I would suggest to everyone, the RTA won't put anything in writing and most don't have a clue how many cylinders their own car engine has but will gladly dictate what hoops you should leap through, engineers only want your money so get you projects registered as a bland conversion, stock motor, stock frame. Once registered do whatever you like and don't make yourself obvious.