Drivers are now wholly comfortable in Gen3 cars thanks to ergonomic revisions, with parts in volume production.
Chassis kits are gradually being sent to teams, with Erebus Motorsport having completed its first.
Gen3 began in earnest earlier this year, with some drivers later raising concerns about visibility and comfort.
Supercars went away and revised the chassis, with taller drivers citing leg numbing and poor visibility.
Seat position and pedal placements were adjusted, with drivers pleased with the end result.
Of 25 active drivers, 10 are over six foot tall - Shane van Gisbergen, Thomas Randle, Jake Kostecki, Nick Percat, Chaz Mostert, Brodie Kostecki, Jack Smith, Andre Heimgartner, Mark Winterbottom and Scott Pye.
Van Gisbergen (188cm) and Brodie Kostecki’s (189cm) feedback has proven critical in cementing the ergonomics.
Supercars later enlisted Garth Tander, who comes in at 192cm, to also put the ergonomics to the test.
The revised chassis centre section ergonomics is now in volume production.
The final design of leg protection and cabin interior is nearly complete, with drivers happy with the common seat mount.
Wet weather at Sandown also offered a chance to run the heated windscreens, which worked "perfectly".
"The drivers are comfortable, but we’ve known that since the chassis was modified," Supercars Head of Motorsport Adrian Burgess told Supercars.com.
"The leg protection and final cabin is being completed now.
"We’re honing in on the little things that we’ll need to make decisions on."
On rare occasions, drivers have suffered foot burns due to heat soak through the front firewall into the pedal box.
That is now set to be a thing of the past with Gen3, thanks to pedal box and aerodynamic changes.
The pedal box, which has also been signed off, is mounted on linear bearing rails and is adjustable by the driver.
Supercars is also targeting a throttle pad to have better thermal insulation properties.
The Gen3 cars won’t feature a long undertray, which will have a double effect of slashing downforce and improving airflow.
The Gen3 prototypes have been taken to nine different circuits in a mixture of weather conditions.
The cars have yet to turn laps in extreme heat, but Burgess is confident drivers will be more comfortable in the cabin.
"We haven’t run the cars on a really hot day yet," Burgess added.
"But the signs are, because of the air flow under the car is completely different without having a diffuser.
"The air flow is far nicer for the driver in terms of cabin temperatures."
The Gen3 prototypes will return to a race meeting at October's Repco Bathurst 1000.