How hard is it to put on new brake pads on a 1970 chevelle and can I do it myself?

Shouldn't be real hard to do. Get yourself a Chilton type manual and you're all set. Personally, here's how I'd do it.
1)Take wheel off
2)Get a big screwdriver. Put it through the "window" in the caliper and into the vanes in the rotor. Pull towards you. This will compress the caliper piston.
3)Use 3/8" allen wrench to take out caliper pins.
4)Replace pads.
5)Put everything back together and go to other side.

Should take about a half an hour.

Jeff

You can't just replace the pads, you have to resurface the rotors FIRST if you want to put on new pads to create a new surface for pads to wear on correctly.

Also cut up a metal hanger and make hooks so your calipers aren't hanging down, and after when everything is put back together, pump the brakes a couple of times and make a couple of hard stop to break them in, but make sure you can stop in your driveway first.