Rear drum to disc brake mods?
 

Has anyone out there swapped late model rear disc brakes on their k1500 truck?

Do it. Its a nice upgrade. You will get a little more braking power.

What donor vehicle is required for the swap and will I need a new master cylinder? BTW my truck is an extended cab z71 with single piston disc up front and drums out back. Also, I noticed a late model tahoe at the junkyard.

Well the tahoe uses rear disc's but they also use coil springs so you would have to do a little fabrication to make that work. Try to find a rear end off another truck that will just bolt up and go. Like a 99-06 HD. Try to match the driveline too. Like the driveshaft and transmission.