Could a Advance RL-140-tp rapid start ballast a 50W DX/45-46 lamp? Do you connect the blue and one red lead to the lamp  or does it need the common white wire .

Rapid start ballast is 430 mA - 460 mA lamp current so it will under drives the the lamps.   Best ballast for 50 watt MV is a 39 watt MH
Ballast as lamp be right on Spec with 670 mA.   Next would be 58 watt preheat ballast on 240 volt.  Otherwise there not much oprions
That runs a 50 watt MV fully.  Unless your willing do some trial and error useing a small cap value on a single lamp F48HO ballast to knock down the lamp drive current for the lamp needed to run right.