The way I see this car, it is more like one of those MGA 1600 Deluxe models (the TC cars they built with pushrod engines after they ran out of TC engines).
Many people consider the Deluxe to be the best street MGA since it has the less troublesome engine but the good brakes and the c/r gearbox.
$20,000 could be a fair price for a nice MGA Deluxe so this car isn't too far off that point if it really has a TC VIN plate....probably worth about the same true value as that 308 in my view. Both great cars but for very different reasons.
As always, value is partly in the eye of the beholder. To be truthful, a new Miata is surely faster and better than either of those cars (and yes, I know that's not the point!).
If I were to buy an MGA (and I am "sort of looking"), I'd look for standard 1500 or 1600 roadster. A decent one can be gotten for $10,000 right now....actually, a good value. By the way, I sold a tatty but running '56 MGA roadster in '69 for $60.
When Otis Chandler and Reggie Jackson started collecting American muscle cars in the 80s, that's when their value took off. I never understood it.
By the way, we had four gorgeous Twin Cams show up at the Pittsbugh VIntage GP this year, plus a Deluxe Coupe'. Despite the reputation of being a headache, that Twin Cam engine looks stunning!