Got a WRT54GL here that runs on a recent DD-WRT build
Mar 29, 2011 [DD-WRT] Reboot my computer remotely? - Linksys Mar 26, 2009 Installing DD-WRT on the Linksys WRE-54G - Jozerworx Latest version of DD-WRT available here (dd-wrt.com) or here (Jozerworx mirror). Checking to see if you have a Revision 1 Device. Linksys made three hardware revisions of the WRE54G. For the most part, they look and function identically, but the important distinction is that DD-WRT can be installed only on Revision 1 devices (hereafter “v1”). Got a WRT54GL here that runs on a recent DD-WRT build DD-Wrt is under development and the recent DD-WRT v3.0-r29837 mini (06/06/16) does run quite well on the Linksys WRT54GL. Installed it 12 days ago and it just runs and runs [1]. Yes it is a beta branch, but I've been on the beta track on a variety of builds for over a year and never had any issues.
Tomato Firmware | Polarcloud.com
Jul 11, 2017 WRT54GL MAX232 Serial - DD-WRT Wiki Serial port on a Linksys WRT54G/GL router using a MAX232 interface IC . This brief tutorial describes how to add two standard RS-232 serial ports to a Linksys WRT54GL router; the same is applicable to several other models based on the same hardware (WRT54G line et all).
Linksys WRT54G series - Wikipedia
Zen One: OpenVPN and DD-WRT on Linksys WRT54GL Jan 16, 2008 Linksys WRT54GL + DD-WRT software