The source code to Hack was posted onto usenet back in December of 1984:

From: [email protected] (funhouse)
Newsgroups: net.games,net.sources
Subject: Hack sources posted
Message-ID: <[email protected]>
Date: Mon, 17-Dec-84 09:11:48 EST
Article-I.D.: mcvax.6238
Posted: Mon Dec 17 09:11:48 1984
Date-Received: Tue, 18-Dec-84 07:04:44 EST
Organization: CWI, Amsterdam
Lines: 20
Xref: watmath net.games:1303 net.sources:2185

I will post the sources for Hack to net.sources.
They come in 10 parts; the total source is slightly over 400kbyte.

Hack is a game resembling rogue (but much richer than the versions
of rogue I have had access to).

The game runs on all machines with sufficient address space:
$ ls -l /usr/games/HACK
-rws--x--x  1 play       159744 Nov 10 19:09 /usr/games/HACK
$ size /usr/games/HACK
text	data	bss	dec	hex
106496	34816	29264	170576	29a50
but if you are unfortunate enough to have a backward C compiler
(without structure assignments or bitfields or functions returning
structures or with only 6 significant chars to an identifier)
then you'll have to work to get this running.

I am happy with mail, but will be abroad the next four weeks.

Good Luck & Happy Hacking !

Oddly enough the full source code to Hack had been lost.  Even the Nethack Wiki didn’t have the full source code, although thanks to the UTZOO archives by Henry Spencer, I was able to look through enough of the tapes since I had the date and subject in hand, and I was able to pull out the entire thing.

I’ve added a package tape for SIMH, as it builds and runs on 4.2 BSD out of the box.

It’s really cool to have saved this from the digital dumpster, although it was there all along.  And thanks to others for at least pointing out that part of it was missing or I’d never even look.