My door caps are 50mm wide and nominally 50mm high (they thin down near the dash) and the dash capping is 50 x 35ish mm. All of them have had the corners rounded over using a router bit.
Then it was good old fashioned sanding. Lots and lots of sanding.
They're attached by these
http://www.ebay.co.uk/itm/SCREW-HEAD...9#ht_967wt_902
With some bolts from the inside of the door. The dash is held in with the same things, but rather than bolts I made some studs that screw into the inserts, and then once it's in place some nuts on the back.