1970 T/A with factory rally gauges. Oil pressure gauge goes from L to H with marks or lines in between. How much PSI is each line and what line(s) are normal cold and at full operating temp?

Normally there's not an exact spec, merely that a mid-range reading is OK.
Production variances (engine, wiring, the gauge itself), oil viscosity, RPM, and temperature also affect it.
If you want to assign a # to each hash mark, you'll need a mech gauge for comparison.

Years ago, 911 gauges had readout #s, and some owners would annoy the Service guys if their gauge differed from what they thought they should be reading.
Porsche removed the #s, and the official line was "if it's in the OK range, it's OK, now run along".

Looking more for what PSI each increment indicates. From memory mine usually ran in the middle or just slightly under the middle of L and H, but today it ran one mark under or 2 up from L. Just wanting to make sure all is ok.

IIRC the oil pressure sender is an 80 psig sender. So with four divisions I would think that each division is about 20 psig.

If you are worried about being ok run a mechanical gauge tee in and compare. The factory gauges are all over the place. On my 69 Charger straight up is 40 psi. Is it accurate I do not know. So if straight up is 40 divide the 0 to 40 and see what each should rear. Example 3 notches between 0 and straight up would be 10 psi per notch.

Check the connection to the sender.
Mine was reading low, the wiring was frayed and about to break at the terminal.
Once I soldered the lead, back to normal.

So I'm around 40 PSI in the 2000-3000 RPM range. Is that ok?

Rule of thumb 10 psi for every 1,000 rpm.

No way the factory gauge is linear. If you want a true reading connect a good gauge. Same with the temp and tach. I have a E body with the ralley cluster. The tach is of 5-10%. The temp and oil pressure always read on the 1st mark. I know the engine has over 50 psi.
Doug

Depends what you are talking about. If you look at the gauge itself, the spacing between divisions is not equal. The gauge scale linearizes the reading.

also, there is an adjustment on the gauges to make them more accurate.
i "think" i remember reading that in the FSM, but don't quote me..............