I think there is a list of suggested replicas in another thread, possibly one of Russ's. Here are a few items, not all of which are casting projects:
indicator bracket mounts for the right side of the carriage (to fit on a dovetail slide, just like the left side). Monarch used to make them. The existing clamshells will fit the bracket.
bodies for taper attachment micrometer adjusters. If the bodies were available, and someone could find the right source for the gears, it would be possible for anyone with the skill to make a reproduction...
light brackets that attach to the rear of the drum switch cavity, like the ones that lathehand made - see his post.
travadial brackets
cast aluminum chip covers for the rear of the cross slide
tool racks for Aloris tool holders, that attach to the rear of the base casting, similar to the Monarch racks (for the Monarch tool post holders), with slots for wrenches, alan wrenches, etc.
replacement fingers for steady rests and follower rests with ball-bearing ends.
Jarno taper adapters
Cross slide dial indicator housings, just the castings with plans showing how to complete the project.
-Dave