The oil is taken up into the block and delivered through the block's main saddles, in through the top bearings and crank journals where it then also reaches to the rod bearings and their saddles. All the while it's also being pump through the front end of the block, into the timing assembly and on up to the top end through the cam, bearings, and bathing the valve train assembly. All of this is by means of the little holes/ports you'll find machined into the moving parts. It makes more sense if you were to actually see it all.
Anyway, a block in the oil galleries would increase oil pressure....not lower it. And, it's not the pump that creates the pressure, it's the resistance to flow within the motor. There's the relief valve on the oil pump that's designed to open in the case of excessive pressure. If it sticks open, the motor will have trouble building pressure.
There are a number of reasons you could be experiencing low pressure....the relief valve only being one. First, verify the sending is working properly and has good connections. Also, read this link here:
It will explain more than I can (rather, want to....
) in this post. Me fingers are lazy today. Stho stharry!