Two important choices: for AMC boxes, the lower lug is forward to alter the angle of the box, mounting lugs may be different width. BigSid fitted a Norton box to his hot Comet, and wrote about fitting it, perhaps ask Matt or check if details are on TheVincent.com.
If you choose Norton, do you want to use a Norton clutch (single row chain) or Commando diaphragm clutch with triplex chain or convert to belt? For this, the mainshaft is longer with a circlip groove for the diaphragm spring. Don't panic, Norton shafts can be interchanged, various lengths were made to give different chain alignments. Avoid 1956-1960 boxes, the ratio set is peculiar making replacement gears difficult. Post 1960 boxes have a modified ratio set, slightly closer, which remained in use for most subsequent machines (barring a higher second gear for later Commandos to ease meeting noise regulations...). Be careful with Mk3 Commando boxes, the gear shift shaft exits through the primary drive case, not on the right.
There are lots of ways of altering the ratio set, due to interchangeability with racing cluster and many of the pre AMC gears can be made to fit.
If you choose Norton, do you want to use a Norton clutch (single row chain) or Commando diaphragm clutch with triplex chain or convert to belt? For this, the mainshaft is longer with a circlip groove for the diaphragm spring. Don't panic, Norton shafts can be interchanged, various lengths were made to give different chain alignments. Avoid 1956-1960 boxes, the ratio set is peculiar making replacement gears difficult. Post 1960 boxes have a modified ratio set, slightly closer, which remained in use for most subsequent machines (barring a higher second gear for later Commandos to ease meeting noise regulations...). Be careful with Mk3 Commando boxes, the gear shift shaft exits through the primary drive case, not on the right.
There are lots of ways of altering the ratio set, due to interchangeability with racing cluster and many of the pre AMC gears can be made to fit.
