that's not unusual for any car of this age. Wheelbase each side is the first thing you measure when starting to setup suspension for a race car. In this case you can correct it with adjustable castor rods. Machine them down and extend the threaded section a few inches. refit with nuts either side of the bush to allow the castor to be adjusted.

Also renew the leaf spring front eye bushes (they will be worn), and check the alignment of the diff in the body.