However, Speedcafe has been told that, of those two vehicles, only Fraser's #56 Mustang has hit the track, with Cameron Waters behind the wheel.
That Waters would have enjoyed seat time is not unusual in itself, given Supercars rules allow him as many as 10 laps on a rookie day (per Rule D1.3.5), but it is thought that he is driving the car as part of engine work and/or aerodynamic testing.
Notably, Supercars engine expert Craig Hasted was spotted carrying throttle bodies in the Winton pit lane.
However, multiple sources have also advised Speedcafe that Tickford/Waters are in fact performing aerodynamic work on Supercars' behalf.
Both Hasted and category Head of Motorsport Adrian Burgess are present at Winton today, and the Tickford garage is said to have been closely guarded by its crew during the day, including the unusual practice of shutting the door between some runs.
An official parity review was announced last week, apparently following a routine post-event Gen3 Technical Working Group meeting, with higher-level talks understood to have commenced yesterday morning.
While engine performance was a bone of contention during pre-season, resulting in a ‘speed test' being held during February's ‘mini VCAT', and then again when Chevrolet teams became the dominant force from Event 2 of the season at Albert Park, aerodynamics was thrust back into the spotlight as an issue at Hidden Valley.
Track time at Winton with one of the category's leading Ford drivers would be a valuable opportunity to gauge the performance of aerodynamic tweaks which homologation team Dick Johnson Racing and Supercars may be mulling over.
It is likely that there will be some sort of parity tweak before the NTI Townsville 500 on July 7-9, with competitors expecting to know more by the end of this week.
A number of Dunlop Super2 Series teams planned to test at Winton today, with some persevering but others having already packed up after a damp start to the day.