This is an original Mallory YCM 278AZX dual-point distributor, a popular performance upgrade for British cars using Lucas distributors. It will fit Jaguar XK120 140 150 Mk I 2 VII VIII IX X 3.4S 3.8S 420 420G 240 340, Austin-Healey 100/6 and 3000, MGC, Triumph TR6 and other 6-cylinder cars which used Lucas distributors.
The Mallory system offered dual points so the likelihood of failure from corroded or closed points was greatly reduced. This is a really high quality item, probably made in the 1950s. You can still get new points and caps for vintage Mallory distributors, and in fact, the company is still in business.
This one is in good condition and looks to be ready to install.