Dear folks, I have just been down the shed stuffing around with Comet gearboxes, and thought I'd pass on the following priceless information. (and since price is a function of worth, draw the inevitable conclusion). The proper gearbox is type G97, followed by a month/letter and year/numeral code. The correct mainshaft is 11.3" long and is threaded 5/8"x20t.p.i. at both ends. The boss at the drive end on which the clutch centre sits projects about .735" from the inboard shoulder. The 1/8" slots for the clutch centre go all the way through the shoulder . The bottom cast boss on the shell which takes the 5/16" CEI adjusting bolts for primary chain tension is 2 5/8" wide and inset about 3/4" from the outer face of the output bearing housing face. The top pivot lug is about 2 7/8" wide and is similarly inset 5/8". Large Panther gearboxes, type G42. are identical EXCEPT for the mainshaft, gearlever and kickstarter. Another gearbox I recently found has different offsets on the top and bottom lugs on the shell, but I should be able to compensate with a suitable lash-up. It seems to be type G10 A47, so I knew it couldn't be off a Vincent. This drivel is prompted by a recent ebay listing for a Comet 'box which obviously showed the wrong "new mainshaft"-at least as far as I could tell. The correct inner and outer casings have one more bolt below the kickstarter than the CP type. The correct casting numbers for these are 4-520 and 4-521.