Dont. Unless you (I mean YOU) plan on tearing it down COMPLETELY, rebuilding EVERYTHING, rewiring EVERYTHING, just walk away.
My 87 Wellcraft Scarab was sunk in 89 or 90, until 2 years ago when ALL of the wiring was redone I was still chasing electrical gremlins. Have it sorted out now, but we didnt realize it was as bad as it was.