I think that I would bolt a long roughly 1" or thicker by abot 7" wide piece of aluminum to the mill table and mill in "L" shaped 5/16 wide by 1/4" deep grooves and as many as my chunk of aluminum would hold. I would hinge a hold down plate over the short legs and part of the long legs, secure with cam lockdowns of some kind through slots in the hold down plate. Using quick change tooling, I would first Centerdrill and then stub drill the pin hole. I would use colbalt tooling for both. Much less chance of a ruined hole and your drill will last longer. I would also look at the New Lube coolant system from SwiftCarb. This will extend your tool life by quiet a bit and avoid coolant splash with your open mill.
Your program for the slots will give you the dimensions for your drilling operations. The slot for the short leg could be just a groove lengthwise down the bottom plate. intersected with 90 slots for the long leg.
Hope this helps.