This is the 1957 Triden, made by Ron Tonkin. It has a Triumph Renown chassis, and a Holden grey motor, as well as gearbox and diff.
That is indeed the car, although some of the facts you quote differ from what I have.
For the point I need to know:
Who originally built the car and when (not 1957)?
When was it re-bodied by Ron Tonkin?
What chassis is the car based on (not a Renown)?
Locked for you to dig deep!!