The way i understand it you have to have your car signed off and get the okay from an engineer when there is a change in engine size. SOooo what happens with a old Escort? The Escort came out in 1300,1600,1800,and 2000 well rs2000 basic same shape.Do you still to go through engineering process. It's the same body.[can understand the change in engine number cos we also have to do that and roadworthy.CHECK this does this chap have to go through the process https://youtu.be/nAaSUAfsMPM Nice car by the way

If the chassis came with a bigger motor it is ok to put in without cert cause the factory/manufacturer engineered it for that motor.

Depends on what State or Territory you live in.
As it's got a Victorian Club Permit number plate try Vicroads website which shows the regs that apply to individual modifications.
It will require a Vicroads approved Engineering signatory to sign it off.

I thought that regardless of if it came with a different (larger) engine that anything more than a 20% increase needs a mod plate.

Cause wouldnt some cars have different brake/suspension setups than ones with different(heavier lighter) setups?

Maybe ring a local engineer/certifier?

My friend with a torana just went through it,was a 6 changed to an 8 The cars had a factory 5.0 v8 Still had to be mod plated. For Queensland anyway

The NCOP is public. It may say the same things as above (any engine factory fitted is allowed, but must be engineered if exceeding 120% of original power).