Mine was a 71 vega - piece of crap. Got it for supposed good gas mileage - would have been far better off with a late 60's mustang with an inline six that was my other choice.
The Cosworth - had to read up on it- very limited production (75 and 76) only 5-6,000 of 'em built - and the engines were waaaaaaaay different than the production models- all hand assembled.
Here's the sickipedia reference on the chevy vega ....
The Vega received praise and awards at its introduction, including 1971 Motor Trend Car of the Year.[1] Subsequently the car became widely known for a range of problems related to its engineering,[2] reliability,[3] safety,[4][5] propensity to rust, and engine durability(mt: absolutely horrible - 50k miles and kiss it goodbye). Despite a series of recalls and design upgrades, the Vega's problems tarnished both its own as well as General Motors' reputation. Production ended with the 1977 model year.
I'd say that was a pretty accurate assessment of the production model vegas. The cosworth's had a whole different engine - designed for racing, and far more durable. GM was trying (and failing) to push their crap production models by showing how good a car the Cosworth was. The public didn't buy the bait and switch. Vegas discontinued in 77.