A carb from dealer would have cost more the car is worth anyway.
The original Solex downdraft is very reliable and lasts well, unlike the
1.7L engine and the older sidedraft stromberg on the 2L. Are you sure it needs replaced. Normally a good strip down and clean sort them out. Maybe service kit, replace diaphrams floats at the most. I have scrapped several cars with perfectly good carbs. Any carb from 1985 onwards will do I think. Get one from any 360 except GLT or GLEi (injection models).
Is the engine in good service overall? Clean breathers, new ignition parts, properly adjusted carb. It should run well, age is no excuse for bad running in these cars.