To re-ring the engine you will have to remove it. Given the abuse that engine has suffered it's not worth just re-ringing it. It would need a complete rebuild which is probably not worth the money. If you're going to pull the engine, just put in a known good used engine.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13