I have a 241 from an 89 3/4ton suburban. The question I have is I am preeping my truck for a drive from CA to NC and I have no speedo. I was going to put a Mech speedo but my tcase has an electric plug for the speedo an the tail end. Is there an adapter I can buy so I can use a manual speedo. Or do I have to buy the universal gm plug for an electric speedo and a electric speedo. Does anyone have that plug or any suggestions.