the TFTP recovery is documented for 1.5, we can't be sure it works in 1.3, unless you can find a post confirming it (I haven't looked).
Current versions of the TP-Link firmware for this router, at least in the US, reject custom firmware and refuse to flash it. If your TP-Link firmware is too new and rejects the OpenWRT firmware file, even after giving it a sufficiently short filename, follow this procedure to install an unlocked TP-Link firmware:
Obtain the TP-Link unlocking firmware. It can be obtained through TP-Link support, and is also attached to this post on the DD-WRT forum, although registration is required to download it from there. It may also be in IPFS.
RRQ from 192.168.0.86 filename wdr3600v1_tp_recovery.bin
The device is searching for this file. Now, I rename the file tl-wdr3600-webflash.bin in wdr3600v1_tp_recovery.bin. The device take some time and then, dd-wrt is booting again.
What should I do? Please help me, step by step ...