Hello, I've got a '67 220 with a j-type OD & 4.56 gears; the speedo reads around 15 mph high around town, 30 or so on the freeway. I'm told j-type ODs will accept different tooth speedometer gears; I've got a 20-tooth in there now, if I were to find a 19, would that make the speedo better or worse? Where would I look? Thanks!