I had the same experience on Blitz's 2GM. I first tried both a long 1/2" breaker bar as well as a very low end 1/2" air impact wrench. Started by using penetrating oil and removing the 2 10mm bolts holding the lift pump on the block. No dice. Pulling a lift pump banjo bolt and using a much stronger 1/2" impact wrench made quick work of it.
-Chris
