They are a different thing altogether.
They are derived largely from the vehicle rules that appeared in
Grim Tales, but there are some fundamental differences there, as well.
That said, they are perfectly compatible with both
Spycraft and
Grim Tales -- you can substitute these rules for their chase chapters almost seamlessly.
I happen to think they're more complete, more consistent and more fun than either of those rulesets (the chase portions I'm talking about), but then if I hadn't, I wouldn't have written them.