rattling or knocking noise

[chevyman]

I have a 82 920.I have had a noise in it for some time I never could find out what it was. But one night I was coming home with a buddy of mine and i thought the thing was coming apart on me my buddy was about 20 feet from me and he even heard it.It sounds like it is coming from down low in the middle but not sure any suggestions on what it is.
                                               thanks Bud

[bstig60]

R there any metal filings in on the oil drain plug or evident in the oil? If its low in the engine, it could be rod or main roller bearings. The only way to know for sure is a tear-down and  then rebuild. If you think this is the problem, I would look for another engine on Ebay or at a salvage yard and just replace it.