Bad news: I can't beat up 128 blocks limitation. It seems, that at that distance tile entities unloaded from client world. I must use something like a "world anchor" to outflank that limitation, but i still dunno how. I'd better make entity on batteries to dig holes any deeper.
Good news: Ldog, you have your "reverse mode" button in gui. Download the new version.
I think it's fine as it is. Without some method to automaticly suck up the blocks (basicly making this a horizontal quarry) it would probably be bad to leave this thing running for longer distances with a chunkloader (and that's assuming you can autoload in more stacks of mining pipes with a hopper/tubes/ducts/etc but I haven't actually tried). Having to move it every 128 blocks really isn't too much of an ordeal.
It would probably be easier (and less performance impact) to make the unit itself mobile (like the railcraft tunnelbore)
Retract works. Loses a few pipes when you wrench the unit, since it seems to always leave 1 or 2 out. I was trying at first to wrench the shield, which didn't work. I stumbled onto something, if you place the shield while the unit is in retract mode, it will place the shield on the wrong (opposite) side of the unit. Wrench works as expected on the base unit (rotates, rotates opposite with shift, picks up unit and contents). Oh, and the fixed placement facing works.