1953 Plymouth Cambridge Flat head 6 engine. Nothing fancy or modifications done. All orginal. Got car running/driveable but it sat outside for about 15 years under a tree before I bought it.
You could or you could backfeed the hot out of the block after removing the thermostat then reverse the flow after.
Flushing tends to be needed if it is overheating, as you have not mentioned any issue like that then if it is running fine then just change the coolant and put in fresh antifreeze or anticorrosion as specified.