I recently rebuilt my 1978RS brake calipers. Biggest hassle was getting the dust boots installed without tearing them. They can be a very tight fit, tore 2 of them. Brembo dust boots are a lot easier to install than these ATE dust boots.
What worked for me was fabricating a wood block so I could evenly press the dust boots in with a big C clamp. I used a hole saw kit to make a round plywood disk and then a smaller hole saw to make a shallow recess to clear the brake piston. Chiseled out the small recess to maintain some strength and thickness in my wood block.
Worked like a charm, clean and grease lightly the contact points of dust boot to caliper, they can get rusty.
Hope this helps someone get there faster than I did. The old ATE brakes can work well if maintained properly.
Trick to adjusting the ATEs is to clamp the brake lever hard and then rotate the adjusting screw clock wise and counter clock wise until it feels the spot between resistance points, i.e. least resistance.

J in Portland