Between my family and friends we have a variety of different sleds. Each time I went to get items like belts or spark plugs it got to be a guessing game of what to purchase, so I put together a list that I call my Snowmachine Cross-Ref.
I listed all my machines along with my brothers and a couple friends as well. The list shows the type of belt needed for each machine and the physical size (length and width). It shows the OEM part number and the Dayco and Gates numbers. Spark plugs show NGK, Champ, Bosch, Autolite, and AC Delco. I've been running Champs in mine lately, so it is good to have the cross-reference as a reminder of the Champ number since most sled manuals list the NGK number.
Spark plugs are pretty standard, differing only in the heat rating, which in a pinch you can use a BR8ES when you normally use a BR9ES, for example.
Most of the belts are pretty close in length, but the difference is hardness of the belt. For example, you could use a Tundra II belt in a Summit 600, but the Summit will tear it up really quick. But the point is, you can use it to get the Summit back to camp.
I saved mine in PDF form and it easily loads onto my phone, so it is always with me.
1996 Skidoo Touring E 380
1995 Skidoo Summit 583