250 inline running hot at highway speed

[ViviensTractor5110]

Ok boys....here we go,
Bought my 69' stepper...ran great around town...but always a little hot on the highway....55-60 mph it creeps into the 220 range....so after a cab swap and lots of body work...I've been driving her again...trying to increase drive ability I yanked the housing...no thermostat....ok.
So I dump a 160 in it and it's only mildly better.
Is this a dwell time in radiator issue that a more restrictive thermostat may cure? The PO was a tool so there's no telling what his motivation was...and for good measure there was a gob of purple gasket maker snot that came out of the rad drain cock when I bled it down.

Your knowlet is always appreciated