My machine is down for a little repair/mod or I would quote you for one, got some 25mm alu in the shop. I'm sure Jonathan will be along soon to have a look at it. My plan as well was to do some motor mounts for ebay perhaps but we will see how that goes.
I have had a play with your dxf and I think you may have a problem with getting 5mm bolts into the holes. I take it you would be using a 25 to 30mm long bolt depending on the thickness of the tool post you are bolting on to. You might need to reduce your outer diameter a bit to be able to get the bolts in without them hitting the side of the mount. But then again you could always mount studs in the tool post then just fit nuts to clamp the mount to the post. Might also be better to make the holes 1mm larger diameter, this will give you a bit of adjustment. The 71mm pitch isnt a problem, you can just mill a drilling jig to get it spot on if you really want to.

Ian