Jay can answer specifically but most engines and DLL's are built as i386 (32-bit) binaries. There is no reason to build 64-bit versions because there is no advantage to it and more than likely it can actually be detrimental to the engine's performance. This is due to the fact that pointers will be 64-bits and carrying them around in an application that doesn't need a huge chunk of memory confers a bandwidth hit where a cache miss and memory accesses are concerned. Quake 2 doesn't warrant a 64-bit address space and expanding it to use more objects or entities to take advantage of that increased memory space will make it not-quake2.
You can download my precompiled version of Quake2 for Linux, which is based on AprQ2, here:https://github.com/jdolan/quake2
Your avatar and the term "slackware" reminds me of my high school days, haha! I used to be into the SubGenius stuff back then. Had countless blank tapes that I filled up recording episodes of the Hour of Slack off the Georgia Tech radio station, as well as the local show Bob's Slacktime Funhouse run by Rev Swoozie the Floozie and Rev Dr Nolan Voyd. I'm sure I still have a few in junk boxes in a closet around here. I know I still have my copy of the Book of the SubGenius. It's on a bookshelf with all my old guitar magazines and guitar tab books. Pulled it out a couple years back to have something to read while taking a shit. Good god, what a collection of poignant pointless weirdness. Me and a few friends actually made it up to New York back in Summer 1997 for the X-Day drill. Had a fucking BLAST! Really wanted to go THE X-Day campout the next year in 98 but couldn't find anyone to go with. And then after high school, I just kinda got so wrapped up in other shit that I forgot all about the Church of the SubGenius. Pretty crazy to see that it's still going strong after all these years. Ivan Stang looks like a fucking old fart now, haha!