a few years ago i had a splitty and I'm sure there was a website i went to see if my engine/chassis matched (it didn't) - was i dreaming about this website or do i need to get a birth certificate to check? ta
Birth certificate it the only way as far as I know.
You could check the build dates of chassis and engine - if they are within a month or so of each other then it's very likely they left the factory together.