Hi Alex!
Got in my life more than 20 different Scott bikes / frames, and that is thruth what Mike wrote about bottom bracket shell - for Scott frame You'll need 68mm shell with bristish thread
About lenght of axle - depends of chainset. Exage 500LX had straight arms same as Deore LX M550 or XT M730 So in my opinion You'll need for them 122,5mm axle Can check thet in catalogues for sure if You want, but shorter axles was dedicated for curved or / and compact crank arms