You have a Klima relay since you have an early W126/M103 car which contains the fuel pump circuit. Jump Pin 7 to Pin 8 with a
fused wire.
I am looking at page 19 on the ETM for reference.
Pumps could have seized easily, they did on my 560 after sitting a few years. Broke them loose with a few smart whacks from a rubber mallet... well the motors ran, but fuel did not pump. Ended up buying two new pumps.
You would be a smart guy to disconnect the fuel feed to the fuel distributor and then jump the pumps. This way you will not pump old fuel into the dizzy, they are sensitive to crap in them. Pump out the old fuel into a suitable vessel and recycle accordingly. Then when there is limited to no old fuel in there, dump in five gallons of fresh.
Make sure you have coolant in the thing and oil. Hopefully you fogged the cylinders before cranking it over for the first time.