The first two things id do … assuming timing is correct.
1. Back flush the radiator into a bucket with water and air pressure and see what comes out.
If nothing
2. Flush out motor while its open and install 160 thermostats and see if it cools down.
As for timing
After nearly 40 years I can get very close w these Mallory’s by ear.
1.Retard it slowly tell it starts growling / mild kinda cam lope sound
2.Advance untell it just starts to smooth out and snug it down
Go for a drive (with you’re ˝ wrench and gloves)
1.If detonating … back it down tell it stops
2.If not … advance tell it does then back it down tell it stops
Be mindful getting zapped and the fan!!
A good load on the motor like a hill helps
That’s about all you can do yourself w no timing marks and a Mallory