3a front brake, toyota conversion

[a Wallace <wallaces@superaje.com>]

Greetings folks,
I am contemplating the possibility of this conversion at some time in the 
future, and I understand that the "opening" for the caliper in the backing 
plate has to be enlarged to accommodate the Toyo. caliper. I'd like to 
enlarge the opening now for this eventuality, in preparation for getting 
the backing plates powder coated. Can someone who's BTDT let me know the 
dimensions of what I need to cut out?
Thanks,
Jim
TS81417 (no bridge pipe if it matters)