I have an 80s Raleigh Marathon that I am building. It's almost impossible to shift because of the severe angle of the cable between where it enters the derailleur body and the anchor bolt. I cannot figure out what I've got wrong. The drop out was slightly bent; but this seems to be miles off. It shifts perfectly after the extreme effort it takes to overcome that angle. Any ideas?

I don't see any other options for fixing the cable. Are you 100% sure it isn't hanging up elsewhere along the run?

Are you friction shifting?

Yes. I can actuate the shifter by pulling the bare cable on the downtube and its just as difficult there; so I've ruled out the shifter.

Looks correct to me. I'd try replacing the housing with SIS type even though you're running friction.

How about a picture from the side, far enough away so we can see the whole derailleur installation.

Is the cable and the housing new? Also, I would clean the the pivot points, and put a drop of oil on each.