I just purchased a Cat 12 9K grader (9k1859sp).  It is a bit of a project as it needs a clutch and a few other parts.  Are there any reccomemender parts vendors for these machines?  I have a parts book on order, so i don't have parts numbers just yet.  I am also confused about the electrical system.  It is an electric start and shows evidence of modification.  There is a chevy alternator attached.  Any electrical diagrams or info on parts sources would be appreciated.    

the dealers are still a good source even for this old gear. but they need part numbers to be truly helpful. so a parts book and service reference are a must. if your a paid member of acmoc you get access to the tech library their is possibly electronic copies of the the books for your machine at least you could get started chasing parts till your hard copy arrives.
just be aware for the older part numbers to show in the cat parts system they often need a zero added after the first 2 characters to make em long enough to be recognised.they need to be 6 characters long. they may have to look on the classic parts list.

google is your friend some part number have been superseded so it can help find the current number. also every item that was or is used by a US government department has a national stock number this can help with bearings and seals and part that are not made by cat or exclusive for cat as it can show what else uses it which might be still available or more common.

cat used hyatt,timken and skf bearings if you look on the bearing itself you should find its actual bearing number.

its not a chev alternator it will be a delco 10si or 12si. yes the primary customer was chevrolet

general gear in idaho has clutch parts for some cat equipment it worth a phone call. they will need part numbers

There isn't a parts book for the No.12 9K in our library yet. There is a Service Manual and a Operation and Maintenance Instructions (OMI) for the No.12 9K  in the library.
The OMI has much info that will save you time and money.
Craig