It depends on the definition of "it."
If you are trying to use the Old Tower as a PXE server, so that you can boot a client from any OS on the server, then yes that is possible and all you would need is a boot manager.
If you are trying to remotely PXE boot the Old Tower from its internal images, and select which one over the network, then that is a different matter. Normally, you would simply change the entire image on the server, but if all of the images are on the client I suppose you could simply have a stub of an OS with pointers back to the local disks (that is, a boot volume on the network and OS volumes on the client). By changing out the pointers in the stub (on the server) you could change which OS boots.