You don't need a mill. I've made 3 different motor/diff/slipper clutch mounts for my 1/8 buggy, and none have had any binding or strength issues. The thing that is hardest to do is to be able to afford the drill bits! A 16mm drill bit will cost upwards of $20.
I'll keep my eyes peeled for an aluminum mount compatible with the Hyper 7.
SH Z-Car, Custom Crawler, 8s Savage, 12s XTM XLB 1/7 buggy, 4wd 4-link rear/IFS Pro4 truck, Custom Hyper 10 Short Course, Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz