I would lean towards the crankshaft being a consequence and not a contributor. Low oil pressure after rebuild is a sign that something isn't right. It should be at its best at that point. Unfortunately at this juncture, the only option is to start again, being attentive to potential issues during the rebuild. This can include being certain that the oil channels in the block are super clean and clear, being to ensure installing the main bearing in the correct orientation (such that the lubrication hole is located correctly), being sure the oil pump itself is in good condition, replacing the oil pressure relief valve, using an assembly pre-lube liberally, confirming good rotation of the crank when installed and without connecting rods attached (smooth with no hard points). And of course, recheck all other bearings, including the camshaft, pistons, rings and bores, etc. Everything should be suspect to suffering damage and needs to be confirmed to be OK.
Sorry to hear this though. I know it's disappointing but I'm sure you'll get to the bottom of it.
Harry