Formula fords have trellis style frame underneath a fibreglass skin, it would work a treat for a T1 build. Many sim racing forums have been selling and sharing game mesh which are virtually a clone of the original.
[img]https://freeimage.host/i/K1Pl7p[/img]
Splines can be woven onto the mesh frame and a reasonably accurate surface model can be produced, then comes the internal structure, suspension, powetrain.
All in maybe 150hrs of cad.
This car evokes the heady days of the V10 era, a 3 litre v6 coupled to an audi trans would be plenty of power.

Here in Australia the road laws impose design restrictions that would create V2.0 T1 with seating changed to symmetrical layout, in the UK you guys could make a perfect clone, certainly a desireable target.

Have a search for the Superlite cars Nemesis, this is pretty close to what you are proposing and used the Audi 1.8t longitudinal engine and transaxle but the 3.0TT would go in there nicely.

The Superlite Aero certainly hits the targets for design, 87k usd is not really locost but gets you a rolling package.
A custom windsheild would be needed in Oz, not sure if plastic is legal for UK.

Well spotted Ugg10.

The Nemesis seems to not be available anyone and iirc the rolling chassis and body work package was $20k when it was available.

You could also use the chassis from the Spire GTR which has been fitted with Audi engines and then redo the body work, maybe. Or if you want a bike engine the TR1ke or Mevabusa or similar from the same company could be a good base.

There was also the Edge Sportscars Devil a few years back, looked pretty chunky though.

Or just get a BAc Mono or a Light Car Company Rocket.

[Edited on 23/12/20 by Ugg10]

[Edited on 23/12/20 by Ugg10]

Our chassis (Furore Formula Cars) would give you a good starting point & a helluva lot cheaper than anything else you've talked about.

We've never used the Audi engine/box, but it would defo go in with some minor mods, personally if going that route I'd start again replacing existing chassis from the passenger seat backwards, it could be a lot narrower than it currently is. It was always a compromise as it was built to take both a transverse car engine or a bike engine

A FF frame would require massive modification to get it on the road in the UK, I know, I did it with the original twin engined Furore, also suspension is too flimsy & easily damaged on our ghastly potholed roads. The Furore was designed from the start as a road car rather than race & is built more substantially for that very reason

No idea how you'd get on with it in Aus, we've got them in 4 countries around the world other than the UK, but never had anyone attempt the Aus market. I know you have to have all sorts of stuff like chassis stiffness which IIRC is actually measured from the roadwheel position, ie taking all suspension into the stiffness equation - long front wishbones from any single seat design wouldn't lend themselves readily to that test