Keep higher idle 1800-2500 range for first hour of run time, minimum 30 minutes. You can shut it off in between the first hour to check things. But when running keep idle up it for first 30 minutes to 1 hour. Spraying the oil pan with radiator with cool garden hose helps a lot too to keep temps down during camshaft break-in. A thermostat is not needed on these old higher compression engines. If one is used, forgo installing the thermostat until after cam break-in so water flow is immediate to keep engine temp down. Keeping the water and oil temps down helps reduce failures. Change oil and filter after break-in period. Run the diesel oil with bottle of zddp plus with each oil change indefinitely.
*We do not worry about fine tuning or setting timing exactly until after cam break-in. As long as engine does not have more than 40 degrees at 1800-2500 rpm do not worry about setting timing exactly until after cam break-in when you can then safely low idle engine. Timing should be set with vac advance hose unhooked and blocked off. These older motors on today's fuel normally like around 8-10 degrees idle timing at around 800rpm. However, fine tuning of ignition timing and carburetor should not be done until after camshaft break-in period. You can spot check timing with timing light while engine is high idling during break-in, but do not low idle engine until after 30 minutes to 1 hour run in time 1800-2500 rpm. Again, you can shut it off anytime as needed during first hour of run time (to check things or to deal with leaks or other issues) but when ever restarting be sure to keep idle up so lifters can get oil splash and spin-in / seat in correctly. When timing is finely set (after camshaft break-in period and oil change), vacuum advance distributor hose should be plugged back in.