If you just want the device to be powered 24/7 without battery, you could use the image I downloaded from a link in the old forum on May 3rd, cannot remember whether it was built by @CHKDSK88 or @lowmaster. However they did not brick my device 
http://sebastianschaper.net/openwrt/openwrt-ramips-mt7620-dlink_dir-510l-squashfs-factory.bin
http://sebastianschaper.net/openwrt/openwrt-ramips-mt7620-dlink_dir-510l-squashfs-sysupgrade.bin
I think the latest version even contained the GPIOs for enabling the USB Hub ports, I don't have specific notes about those though. The only scribble I found on paper was this about MSP430, wanted to make a nice and clean schematic with EAGLE, but then the forum was gone and I never continued 
I think I will have some time next month (one week of vacation after christmas). As far as I remember, I had destroyed the MSP430 UART connection on one device while testing, but I might find the issue with the new microscope soon
By the way, there also seems to be somewhat acceptable support for MT7610E by now, which should probably be included when someone intends to build a new image: