..oil light comes on until about 2000rpm should I worry about this
Yes it would be cause for some concern, as the normal running pressure should be around 60 psi, and about 20-25 psi at idle, the oil warning switch should normally operate at somewhere between 5-10 psi (depends on the actual switch type?) so unless the switch is faulty the pressure does seem to be a bit low?
The oil pump could be worn, or the pump feed ball valve not seating correctly, or the pressure relief valve could be either worn or stuck open?
Being a '73 model it should have the 650 type timing side bearing and big end feed arrangement so the crankshaft seal in the timing cover could be damaged? And it's not unknown for the lip of the seal to blow outwards due to the oil pressure?
Personally I would want to connect a gauge to check the oil pressure.