This year all of theam 388s milling work was done on an homier mini mill converted to true inch using a kit from micromark
http://www.micromark.com
the mill comes with screws that do 1/16" per turn, which requres conversion to do normal measurements such as .060" the kit changed the mill to .050" per turn which helped alot. Thiese are good little mills IMHO my mill has an r8 spindel to be compatable with larger mills, you can get more information on theise at
http://www.mini-lathe.com/Mini_mill/Main/mini-mill.htm
the harbor freight, homier, grizz, ect. mills are all made by the same company in china with only small differences in the brands, color, spindle(r8 or mt2) and accessories included. From all of theise I chose to buy mine from homier
because they were having a tool show near my home and I could go pick it up to save shipping costs, also homier was the cheapest vendor of them to start with. Ok now back onto topic
You can use digital scales as a DRO however their are digital scales avalabe ment for this purpose try searching on ebay for "dro quill kit" I have seen listed scales up to 36" listed and there probally is larger if you needed them.
The readings can be viewed directly from the scales, or you can build an external display such as the shumatech one (I am currently building this one, will post info when completed) for around $250 you can have an entire dro system. Not only will the shumatech unit display the data from chinese scales but will calculate bolt hole circle locations, act as an tach for your mill or lathe, and you can interface quadrature encoders to it if you want to build your own scales.
The chinese scales are basically the digital calipers stripped of their jaws with mounting brackets attached to the ends and to the scale body. What some people have done with calipers is to drill mounting holes in the jaws and use either brackets or directly mount the caliper via the jaws to the mill or maby fabricate a set of caliper jaw holding clamps you could mount to the ways? You can acheve absolute readings via the zero button on most of the calipers you can also use most of the calipers (using the cheap chinese ones here) as metric dro also, could be useful sometime? There are pics of vairous caliper and scale mounts in the shumatech group, as well as the GrizHFMinimill group.
Links to theise great little tools
Minimill Yahoo groups
http://groups.yahoo.com/group/GrizHFMinimill
Shumatech website
http://www.shumatech.com
Shumatech yahoo group
http://groups.yahoo.com/group/ShumaTech/
Homier mobil merchants
http://www.homier.com