My passenger side disk brake grabs and slides the tire on quick stops. The driver side does not slide and the car does not pull to right. The disks are 11 inch GM Metric/Mustang II on a 40 Chevy. They have been on the car for 5 years and have been working well up to a few weeks ago.

I have checked all the lines externally and they look good to me. I am thinking the driver side may be the problem as the passenger side is doing all the work.

Any ideas on where to start on this problem?

You most likely have a caliper sticking. The other possibility is a flexible brake hose that is broken down on the inside and is "check valving". Either is not a difficult fix but diagnosis is just a little time consuming.