In theory no D14/4 speed gear box should be allowed in the Scottish as these were manufactured after 1965, late '66 I believe. Only 3 speed boxes were made prior to '65 in the D7 motor. Don't why later motors are allowed, probably like a whole host of other mods the blind eye has been turned from. So mod away. Blue printed barrel polished and ported, 185cc piston, George Todd ali head, modded clutch, smaller primary gear and probably much more.