vacuum assist brake replacement. on 1995 Chevrolet 1500 Pickup

How hard is it to replace the whole brake vacuum master cyllinder item that is mounted to firewall? My assist is gone. Me thinks it has rust hole in it or busted diaphram, don't know how it is built actually, just thinking of welltrol tanks.

Asked by for the 1995 Chevrolet 1500 Pickup