A pig in a poke
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You really don't know how big a prob it will be. The gear box and bottom end would be my worry. I'll take his word on the top end.
If one gear has gone I would be sussing the others. They are easy to work on but getting the parts might be an issue. The good news is that a wide range of parts over many years will fit.....but time and fiddling. Ditto bottom end.
Lectron carb are great carbs when set up right but getting them set right is another issue. Parts are still available but experience, expertise and advise might be hard to come by. And its not OEM. Where's me Bing.
Check for OEM Amal controls/levers.
Airbox needs to be replaced - available from Jared SW Montesa but by time you get box, cage, filter, connecting rubber and postage don't expect much change out of $250.
New plastic are available. DC 'race' plastics about $200. Good correct NOS stuff with well defined logos in plastics somewhere between $500 and unobtainium - good luck.
Rear shox could be OEM; condition? If shot race shox $1000+.
For my money I reckon $500-1000. I would rather buy Ross's well sorted 414. I don't know how much he wants for it but he'll probably give it away shortly - he's been struck by a dreadful virus that has turned his blood blue; we don't expect him to be with us much longer :'(. That Yamahopping overweight overpowered dinosaur will buck him off and stomp all over him
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