Does anyone know if the SU carbs AUD 521 AND AUD 527 are interchangeable? It looks like the 527’s have something extra on the side of them.

I will be replacing them both in pairs but don’t want to end up with running problems. Its for my 1972 RRC with 3.5 v8.

Is the extra lump on the side of the 527’s auto choke or summit?

All info asap would be appreciated