My son has recently purchased a 2001 Econovan and does not intend using it commercially so the low ratio diff is not conducive to highway cruising. Thirty years ago I had an Econovan and it only took me an hour to fit a Mazda 808 diff centre. This lowered RPM by about 20% at cruising speed. Is such an alternative "bolt-in" diff centre available please for the 2001 model?