Drum to disk brakes

Look around in the threads here on this site. There is plenty of info from people.
For a basic answer there are the kits including Dr Diff. But also LEED and SSBC.
Dr Diff provides a spindle but that requires the use of a later (73-76) upper control arm and ball joint.
LEED and SSBC use an adapter to mount a mustang Kelsey Hayes caliper to a 10 inch drum spindle. They also use the mustang rotor. SSBC still offers the rotor drilled for Small bolt pattern.
Finally you can also find an original Kelsey Hayes system. Watch the adds here as well as eBay they pop up pretty often.