The VIN plate on the door should carry the details. On some late cars there is also the VIN number in the sill of the boot (trunk), but nothing around the seat. For North American cars there was also the VIN on a windscreen tag in the lower corner. Brian
Of my two UK 7's (both manufactured in 1978) I never did find a chassis number, the door vin plates are blank, the USA import (also manufactured in 78) does have it on the windscreen tag.