Iffy.
Layouts is Polyphony's generic term for alternate track maps, ie. Suzuka Full, Suzuka West, and Suzuka East is three layouts.
To my knowledge they've never done an alternate that was an earlier version of a track before. They change the surroundings of current layouts to suit them, adding barriers and cones as appropriate. That a period change requires a larger change in the surroundings isn't a reason to not expect them to be there.
If something is labelled as '85 Brands Hatch, I don't think it's unreasonable to assume that it is actually a reasonable replica of '85 Brands Hatch. If the track was labelled '85 Brands w/ Modern Surroundings or some such, then sure.
Given what we know of PD and their work methods it was also a reasonable assumption that they were going to shortcut it like this, but I think in general if something is made into a retro version, you do it all. If random developer says that their new racing game has '85 Brands Hatch, you expect a full period version, not the '85 layout with modern surrounds.
A 2002 RX7 doesn't become a 1978 RX7 simply by changing the engine, drivetrain and suspension. Sure, it might drive identically to a 1978 RX7, but the fact that it looked like a 2002 would put some people off. You could work around this by only driving from bumper, not watching replays or whatever, but the fact remains that it's not entirely a 1978 RX7.
The same problem applies here. What they've done is nice and all, but they've not entirely made '85 Brands. For people who were interested in immersing themselves in that period of racing, it's a let down.