The parking of the car is consistent IMO with someone pulling into the kerb behind another car that the driver was expecting to be there. This is either because it was SJL meeting someone and she just jumps out to say Hi or whatever, expecting to be out of the car for 15 seconds - hence no handbrake, not parked properly, purse inside, etc. Or it was someone getting rid of her car by driving it to where his own car had been left. He switches cars p.d.q. and drives off, and ten hours later, it's found as left.
Of the two the latter seems likelier, because if she met someone who said
Let's go on to X in my car, she'd surely have said
OK, let me just park mine properly and lock it; or,
OK, I'll follow you; or whatever. For her car to be left like that upon her meeting someone there surely says she was abducted then and there.
Terry makes a good point as usual re the seat position. You have to wonder if anyone ever checked that someone of Cannan's height could or would have driven it with the seat positioned thus. In 1980s Fords (I drove many), you moved the seat by lifting a bar under the front-middle of the seat and then pushing back with your feet. I do hope someone checked that seat adjustment bar for fingerprints in 1986.
Re the guys working in the road, I thought, from AS perhaps, that they were BT guys working in one of those
red and white striped workmen's tents. They'd have set this up either over a manhole in the road through which they accessed the phone wiring, or next to one of those green roadside junction boxes. As has been observed above, they are sort of anti-witnesses. They'd have seen little from inside a tent, but their noticing or hearing nothing out of the ordinary does rather suggest nothing happened.
AS wrote this down in 1988, before Cannan came into the picture. One of the reasons he's valuable is exactly because his early account is
not completely shot through with the later DL / MPS determination to fit this one round Cannan. Cannan could well have done this, but there's a lot about his involvement that's not explained, and he sure wasn't the only rapist who'd been released recently.