This is a cheap china 8" I got a while back and have been working with for a while. I did this thing twice, this is as it is right now and I like it so far. Before, I had the motor directly mounted on end of shaft and it was too long for traveling in the confines of machine. All I have to do now is to make a cover to keep krap from belt and to redo the wires. The wires work as is but I can't run them close to each other or I loose all function with the drive. I really need to cut them off and start from scratch with twisted pairs or something so I can run them in one bundle but I don't know yet if that will be enough.
As for Zero backlash, I have found that it is all in the setting of the worm. The worm is on an accentric and can be rotated into the gear for lash control and then a little stop set is run into stop for same. I found that they are not as quality controlled as I'd like but they are functional. Mine had some binds in the gear mesh, shaft bushings etc. which needed touch up, can't do anything about binds in worm tho except wait for them to smooth out in use. I am using a large servo that I got from Keling and It don't mind the binding at all within reason. If set too tight initially it can and will stall the drive out but that falls into how tight the lash is set. The backlash as mine is setup right now is so miniscule that it is quite ignorable and with use I thing it will get better.
I modified the end of the worm shaft and the concentric by shortening the concentric and machining the shaft then boring a pocket for a roller bearing that I had. This took a lot of wiggle out of the shaft and allowed me to set it up with some preload on the bearing to hold shaft in one position within the concentric.
I have had thoughts of using an indexer already setup with a chuck instead of this thing but didn't. If I get a few bucks ahead someday, I still may give it a try. Maybe my included pics will help with your idea's.