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I'd start by trying to diagnose the problem. 1) Use a mechanic's stethoscope to verify the origin of the noise. A dying water pump can sound like bearing knock, for example. Loose flywheel bolts can cause a similar sound. 2) Wrist pin noise is a "click-click" sound very noticeable at idle. 3) Worn timing gears usually don't "knock". They make a "grinding" noise. 4) If the noise is louder when you blip the throttle, that's piston slap caused by worn rings which then cause worn piston skirts. 5) Verify oil pressure with a known good gauge. If it's lower than spec, the bearings are suspect. 6) Main bearing noise is a very deep sounding hard metallic "thump" that is usually louder when the engine is first started. Rod bearing noise can be similar sound but remains the same volume regardless of rpm. Pull each plug wire in turn; if the knock goes away, that cylinder's rod bearings are shot. If the noise gets louder, it's piston slap. In any case, I'd do a compression test and depending on the results a cylinder leakdown test as well. As long as you have to pull it apart you might as well fix everything that's wrong with it.
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