Couple of things you can check........
Bottom rad hose collapsing when you rev.??
Ignition timing??
Was there a brass orifice plate under the Thermostat??
Fans blowing the right way??
You can swap out the Thermostat for a colder one. Clevos can run quite warm, depending on how thick the cylinder walls are, water pump condition, fan belt slipping etc, etc.
If it's just rebuilt and tight, it will run warmer until it frees up a bit. The twin fans should be plenty.