I had the same problem a few days ago. I bought a new TL-WR841N. You don't know which version you get until it's actually here. Fortunately I was lucky and got a supported version (at least for OpenWRT).
In the documentary of openwrt on which gargoyle is based (so I guess it should work for gargoyle too) router versions are supported until 1.9.
IF you want to take the risk, make sure you have the tools to unbrick your router (PL2303 TTL cable).
I would suggest you try the latest version of openwrt and the flash the latest gargoyle firmware, maybe someone else can confirm this, I read here in the forum that you have better chances to go from openwrt to gargoyle.
http://wiki.openwrt.org/toh/tp-link/tl-wr1043nd