Help - 73 911E injection pump problems

Recently purchased 73 911E, all original. Soon after purchase, started
running horribly, backfiring. Found probable cause - injection pump belt
loose, skipped a tooth or two. Pump had been replaced recently.
In the course of resetting the belt, removed and reinstalled entire pump.
Started engine, started hard and ran rough for a couple minutes, then
stalled and would not restart. Found that fuel inlet and return lines were
reversed. Would not start again, and on further inspection, found that
injection pump would not deliver anything from ports on top - not a drop.
Plenty of fuel being deliverd from electric pump.
Did I kill the pump by having the fuel lines reversed, or do I need to
prime the pump somehow? What could make the pump not deliver any fuel?
Thanks
-Hans Achter