I'm almost positive Rootes engineers knew what they were doing re: track width.
Track width is inversely proportional to weight transference during cornering. Narrowing the rear track width, relative to the front, allows for several things.
1) Lighter IN/LB spring rates in the front
2) Increased straight line stability at higher speed
3) More predictive weight transfer when cornering
4) Induces oversteer more easily at low speeds or high-degree angle turns.
The lighter spring rates in the front dramatically improve comfort...Alpines with worn out suspension components ride worse than straight-axle dump trucks. The increased stability makes the car more comfortable and safer to drive longer distances. Of course, better predictive weight transfer, helps with driving in all situations. And if you don't appreciate oversteer at low-speeds when you turn the wheel and push the skinny pedal down...then I'm not sure why you'd want to own a sportscar of any stripe!
Fortunately, the weight distribution in the Alpine is fairly close to 50/50 and power output (at least non-engine swapped cars) is relatively low. Such that squaring off the track-width via running wider tires in the rear vs. front, doesn't make an appreciable negative difference in handling. The car is sufficiently well balanced and (under)powered that it is difficult to overwhelm modern summer tires let alone R-comps or slicks. Basically, you'll get pretty neutral handling with low-profile modern rubber.