To add to your list of 510 resources: Riley at Lynchburg Nissan :http://www.lynchburgnissan.com/
Unlike a lot of Nissan parts guys these days, Riley speaks fluent Datsun and is very helpful. Other references here show he's a frequent go-to source for parts questions.
Also, the Dime Quarterly was likely the last printed newsletter in a succession of 510 enthusiast publications. Not the usual "club" format, it was loaded with tech articles. The archive site has these available as pdf's, along with related publications, manuals, etc. An index is in the first file, DQ Appendix.xls
https://drive.google.com/folderview?ddrp=1&id=0ByCvxnHNk90SYzc4N2E1MWEtMzg0MC00YTE4LTkxZGQtM2RjODA5ODA1YjU1#
https://drive.google.com/folderview?ddrp=1&id=0ByCvxnHNk90SMzIxZWIwYWYtYzljNy00ZGU2LWI3ODctYzRjMmE0MGY3NTA1#
http://datsun510.com/manuals/