If you can afford it, the Sherline rotary table is a great unit. From a pure performance perspective they just can't be beat. If you are just wanting to try a build yourself for fun or just to save some bucks, thats great though!
I have seen a couple done on the Taig headstock before, some without worm gears. There was even a guy on Ebay selling brutally simple and really cheap to construct rotary axis units made from these, by using the headstock and the stepper sitting parallel to each other. There was a plate drilled to mount to the back of the headstock and to the front of the motor, leaving them to sit side by side. Timing pulleys were then attached - small one on the stepper and larger one on the spindle - and connected with a really short toothed belt. For this application I cannot imagine backlash to have been an issue, though a tensioning idler would be a no-brainer to add to this idea if you felt the need. This may not have enough resolution for you, only having a reduction of more like 4:1 or so.
As for resolution, is the resolution you are talking about necessary for what you are doing, or maybe even desirable? Better resolution always sounds good on paper, but even at only the 72:1 reduction of my regular table, I sometimes have a problem keeping proper feedrate for my tools. Too many steps/rev and the steppers just might not be able to spin it fast enough for you. This is why I also keep a 10:1 on hand when needed.
Don't know what it is you will be doing with it, so just something to keep in mind and consider in your calculations .