The oil pressure relief piston is different from the tensioner. The relief is under a hex headed cap at the top of the pump, pointing to the dside.

The first step is to use a mechanical gauge to test the pressure. Remove the sensor, and use a std. plumbing 60psi gauge with a 1/4" pipe thread male adapter attached. Use a 1/4"npt tap to ream out the block threads to a shallow depth. The sensor will still fit with teflon tape. Test the oil pressure at idle and at around 4k rpms. You want 10psi per 1000 rpms.

I'd send an oil sample to Blackstone Labs to look for bearing metal, too. Much better than trying to eyeball the drained oil.

I'm concerned about the knock. Jasper reuses lots of parts, like oil pumps. It's possible to shim the oil pump relief spring with a flat washer the size of the spring in the hex cap to boost pressure if the oil pump is ok. It's possible the relief vavle piston is hanging in the bore partially open. The bore has a hole in the side which is uncovered by the piston when the pressure overcomes the spring pressure and pushes the piston far enough to uncover the port. The released oil goes back into the pan.

With the mech gauge in place, look for a flutter in the pressure, indicating a bearing with too much clearance. This will require an engine rebuild.