Don't do this at home boys and girls just pay a machine shop the $25 per wheel to do it to spec. If the centre is out by 1 mm that's going to put loading centrifugal imbalance pressure on the wheel bearing and axle causing a catastrophic failure.
I get 8t and live the idea for a track car but if it's not the correct size to fit enough on the hubcentric lip then buy rings and do them to that so the inner is the 69.7mm or so
Jeff Isaacs thanks so much for the reply! I'm gonna do this myself, any instructions you can me and maybe others who see this and would like to try it. So far I've seen your way as being the easiest and most accurate so well done!