A properly working four wheel drum setup is safer than a botched disc install with master cylinder issues. So there is a lot of sense in what Terry says here. Of course this applies to leaving the stock wheel size in place too. If you change to larger circumerance wheels, you put more work on the original brake system than it was designed to take.

If you install a new system, you need to be absolutely sure you have it properly balanced front to rear. You also need to be sure you have plenty of pedal left with a new configuration.

The original brake lines on a 37 year old car should be replaced. Brake fluid retains water that causes the lines to rot from the inside. They become very brittle, even if not rusted. Brake fluid is one of he most neglected maintenance items on a car. Loss of pedal is not something you want to find by accident.