Wow, I wish I had seen this sooner as I don't believe your problem is fixed long term!

Both my father and I had problems with '71 vintage motors overheating. Replaced hoses, thermostats, had the radiators cleaned and everything would be fine....for a while...

I turns out that on both motors (his a 383, mine a 318) they had lots of casting sand that was left in the block! Both motors were original and had never been out of the car when we bought them. After we pulled the motors and THOROUGHLY cleaned out the pan rails/water passages the problem went away.