Hello Sanne,
Good to see you on here
I have attached a print of the C15's in the Canadian Register database (that website is no longer online):
CanadianRegisterDatabase_C15.pdf
It will give you a few references between chassis and engine numbers to work out where the chassis number of your C15 could approximately be.
Hope this helps.
PS: please share a picture of your project in your current state. I will post some pics of when I picked it up in Norway later.