There are problems with a 142 as a track day car....
Overall size is the biggest issue, fancy barrelling into a fast corner and trying to outbrake your mates? It'll do it but there's an awful lot of car to waggle about!
Top speed, well, it's not good is it? Nor is acceleration, but that can be resolved easily by levering a v8 in, and there's plenty of those knocking around SA (is that a Perana Capri? If so that's a good donor!
), see:
http://www.jagsthatrun.com/Pages/Volvo_200_V-8.html
for inspiration.
You won't have to worry about historic modifications unless you start competing seriously, which is one thing myself and S-man have to think of.
I had arranged to track day the 144 this month but had to cancel, which I'm gutted about or I could have told you exactly how they go.
As S-man says, there are better options for track cars, but there are better options for rally cars too*, it comes down to two things: What do you own? What do you want to spend? For me, it's "A 144" and "not much" respectively, therefore the 144 is the play car and will be rallied, tracked, sprinted, jumped over the Grand Canyon etc, and so should yours.
There's always someone else keeping their 142 or 144 mint so as long as you don't wreck a really nice one doing it you should go for it.
The usual order, Handling, Brakes then Power when it comes to souping it up, it cuts down on the crash rate!
Sam
*Yep, I know what things the 140s won, also I know I get beaten by MkI Escorts a lot, but I don't like Ezzies and I can't afford to build a trailer queen rally car to win such as an Alfa GTV or Gilbern GT. I like rallying the Volvo, it teaches me a lot about car handling and I can drive it home. If I enter the London Sydney the 144 will be ace, but the things I'm currently doing would be more competitively done in something smaller.