OpenWrt Project: Linksys EA4500 v1, v2 / E4200 v2
Unfortunately, the newer E4200 v2, which was released after the original, is powered by a Marvell CPU and chipset, which is unsupported by third party firmware, meaning the E4200 v1 is the last — and widely recognized as the best — wireless router that Linksys has produced with third-party firmware support. Linksys E4200 Wireless N Router Unboxing, Firmware Upgrade Sep 30, 2011 Linksys 4200 User Guide
OpenWrt Project: Techdata: Linksys E4200 v1.0
Nov 27, 2015 Linksy E2500 Firmware Upgrade - Download.com
Download Linksys E4200 v2.0 Router Firmware 2.1.41.162351
Jan 29, 2018 DD-WRT Forum :: View topic - Linksys E4200 Firmware Dec 13, 2015