A friend had the heater core clog up in his 59 Savoy. Flushed the heater core by removing both hoses filling it with water and alternating between blowing in each hose which will agitate any debris.Might cross-threading the block plugs have caused a leak that eventually caused your cooling system to run hot?
Removing even such a small amount of scale is an improvement. You don't want any of it lodging in your new radiator and causing a similar problem. I'd also recommend a procedure that was described a few years ago on another thread here: disconnect the hoses to your heater core, attach two cut yard hoses to each end, and pour water through one of the hoses, aiming the other to a drain pan. You can attach another hose from the outdoor tap to the cut ones, but don't run the water pressure too high. You want to remove as much crud as possible before installing your new radiator, and the heater core is one of the places it can accumulate.