the fuel pressure sensor or port if you wish is on the main oil galley in the block, regardless if you have oil on top (which you should since your pressure is > 0) it doesn't mean anything (like he ^ said).
aside of the main bearings (which would be the most likely cause at this point), cam bearings and even rod bearings can cause the same issue and also the lifters [but less likely]. Clearance (or lack of) between the oil pump pickup and the oil pan is another reason for lack of pressure.
if you're testing the clearance between the crank and bearings and it's out of spec then you know the next step, if it's fine then you need to look at other reasons.
another reason could be (and this is a very long shot) an oil galley cap sipping oil or missing (but that would mean 0 pressure) - i think there is one behind the dist chain cover and 1 behind the bellhousing, if it's the latter you'd be losing a lot of oil so that's not likely.
Oil pump was changed so that is out of question.
EDIT: flushing won't do anything at this point, you already took the oil pan out, so there's no gunk on the bottom to prevent the oil from going up the pickup tube. If you had pressure (like normal pressure i mean) and no oil on top of the head then it would make sense to try flushing but in your case i doubt would do anything - if there was something blocking the oil from reaching a bearing or lifters it would make noise but your pressure would be high, this is not your case. You can try but slim chance that it would have any [positive] result.
