Just catching up here. Relevant to my interests as I enjoy driving the golden era Trans Am cars. I wish we had a small block Mustang and Challenger.
Anyway, as I mentioned above, the layout of Laguna Seca has changed considerably since 1970. This is what Laguna looked like back then;
As well, I took a look at the current historic trans am results and verified the cars are indeed running mid 1'40s. While that may seem silly given a GR86 with bolt ons can run similar times, historic trans am racing is more about the show these days. The cars are capable of going faster than they were in the late 60s and early 70s, though. Even so, in qualifying they were running 1'43s
last year. In the races, they're
running 1'46s at best. You can see how the races go in
this in car from a couple of years ago.
The original tyres they ran were treaded like the Goodyear G7, and they keep that rule today. Though technology has changed a lot and modern compounds like the Hoosier TD and Avon's vintage stuff are much faster than tyres were in 1970. Pure compound wise, the Hoosier TD lies somewhere between a CS and SH, and what they ran on back in the 60s and early 70s would be closer to a CM at best. Though the game doesn't always seem to model the gains from large wheel widths terribly well, nor how forgiving bias ply tyres are with the slip angles they run at compared to modern radials.
The cars were pretty crude. If you haven't, Mark Donohue's
The Unfair Advantage is a good read and details a lot of the development of both the Camaro and Javelin. He talks about various things they did to eventually get the Camaro down to under 2600lbs, and handle, while Traco was building 450hp motors. Even with panhard rods and asymmetrical leaf springs to control the rear they hopped around and couldn't go to full throttle in most turns until straightening the wheel at the exit.
This promotional video from 1970 shows how rowdy the cars were.
This one from the 1969 Donnybrooke(Brainerd) race shows a bit how the cars behave as well. If you're bored, there are a number of
documentaries that covered the era at the time.
Anyway, the OP touched on a couple of the issues that leave you chasing your tail with these cars in GT7. Certain tyres do gain more than others with wide wheels, and certain cars benefit differently. There is only so much you can do with a 450hp 2600lb car. It's also worth noting the real cars had zero camber and toe in the rear, four speed transmissions with stock gear ratios and factory rear gear options to swap between, and the engine technology that allowed them to make 450hp while limited to under 5.0 litres also meant they didn't idle and had no torque until 4k. As well, it's not going to model the suspension geometry changes they instituted on these cars to get them to work. In the game we're adding power and grip and adjustability, but not changing the geometry with panhard rods and watts links and custom length arms, etc. All of these are going to impact how close you can get to building a trans am car in the game. The closest you can probably get with the Camaro in game to the original is to build a ~2600lb car and aee if it can make 450hp and spin to 8k without boring or stroking, run a custom transmission with stock m22 ratios, and run zero camber and toe in the rear. Put something like that together and see what tyres it takes to run 1'43-1'46s is probably about as close as you can get. It's not going to be perfect, but maybe get close.
The cars running historic trans am now may not be quite as light as the lightest cars Penske had in 67-68, between not having the custom body panels and having modern safety equipment, etc; but they do enjoy the benefit of modern drivetrain technology and tyres. SVRA rules have the Camaro at 3000lbs, and with modern technology they make over 500hp now. They make a lot more power, tyres are much better, and they go faster than the cars did over 50 years ago. But they still aren't running under 1'40 at Laguna. 1'30 is the modern TA2 lap record.
Anyway, hope this helps.
Related reading;
Ever want to know how Penske and Donohue prepared the Trans Am Camaros?
www.deansgarage.com