I'm pretty much right on track with 67Dart273 (Del)
If it cools fine at speed then that tells us the cooling system is capable, but just not enough air flow.
The clutch fan with the shroud should solve that.
I wouldn't even worry about the condenser spacing, because once that clutch fan and shroud are on there it'll be pulling through the entire radiator surface and all that air will be coming across the condenser and trans cooler anyway.