Glad to hear that you've gotten it narrowed down to one cylinder. I was going to suggest a rebuild of the lift pump, and would likely still recommend that, no harder than it is to do. The parts were readily available from my local Bosch shop, about $45 total. This included check valves, spring, washers, etc. There is a parts diagram around here somewhere. My Bosch guy (Metro Injector, Allentown, PA) only needed the number off of the side of the injection pump. It made a huge difference in the way the car ran, and it wasn't running so badly before. You will need a 30mm socket to finish the job.

Another real improvement came when I changed the diaphragm and seals associated with the governor. It wasn't as easy, but was well worth it. The hard part was reinserting the circlip without dropping it into the pump itself. Mine wasn't ripped, but had become porous and was allowing fuel to pass through it. I read where you've inspected yours. Mine was $80 from Bosch, and readily available.