In Australia once upon a time, touring car racing was modified production racing. Then from 1973-1984 it became modified production racing according to Group C (FIA 3C) rules. Then from 1985-1992 international Group A rules were adopted; after which time the two big manufacturers of Holden (GM) and Ford had a hissy fit and whinged their way to Group 3A regulations - which are still in use (sort of)
Group 3A cars are run according to a 5-Litre V8 formula; with central dimensions being held from the legacy piece of the Ford Falcon AU - FGX.
The wheel base through the centre of the locknuts is 110.0 inches long and 74 inches wide (which was actually still based upon the Ford Falcon XK from 1960).
The engines currently in use are legacy pieces from when the current iteration of the category was drawn up. Fords run a 302 Windsor while the Holdens which did run a Holden 305 engine (after previously running a Holden 308 engine in Group C), now run an Aurora built Chevy 305 engine, GM (part number 10243869) for Sprint Car Spec Racing.
They run a control 6-speed Xtrac sequential gearbox and a spool drive (ie, no differential - just a crownwheel and end gear); which I think qualifies as a dead rear axle (?).
From 2007 the Commodore ceased to be a production shell as the VE was both too wide and too long; ZB was too narrow and too long; and from 2019 S550 Mustang is too low, too short and too narrow.
For Gen-3 they are talking about completely bespoke bits of kit.