This server appears to have been closed source, and I assume the source is lost.

My bet is that OpenBSD's X server has a far better security design, as the server itself no longer runs as root. The aggressive free() also exposed use-after-free bugs never before seen, and OpenBSD has superior mitigations for rop gadget abuse, aslr everywhere, and other exploits beyond the imagination of 1989.

The paper documents problems of Ada, particularly in linking to C (where the use of void * pointer casts was particularly difficult for Ada's type system), and that the Ada implementation had nearly double the lines of code as the C reference.

In the days of 1989, the fastest CPUs were under 100MHz. It is unlikely that any of this code could be salvaged for a modern server, but the accomplishment is interesting.