Glad to hear it's working for you! My goal with this mount was to not require any special holes when using the stock makerslide carriage. I have a new belt attach bracket for the rear but that will require two holes. I've printed it but haven't installed it yet since my temporary rigging seems to be holding for now.
As for widening ... the new spool holder rod came in from McMaster today, the longer belt from sdp-si came in yesterday, I already have the wider base extrusion and makerslide rail (Inventables), and my new handle plates (laser cut by Ponoko) are somewhere between CA and NY... they'll probably be here next week. I'm out of town next week so it'll probably be two weeks before I have photos showing the completion.
For giggles here's a random rendering I made (using j-heads not the e3d's I actually used):