That's a Spica manifold. Adapters are required to mate Webers to a Spica manifold, and the method for sealing the carb throats to the adapters can be trouble-prone. I wouldn't recommend trying to use this.
That one came with the engine - and I didn't like the look of the adapters. I don't have it anymore.
I'd have to locate a manifold for a decent price to swap. The one that's on there works fine except for the thermostat (now).
50 years from now - how are we going to restore a "classic" microprocessor based modern car?? Alfas - 1980 Spider, 1987 Milano, 1976 Spider