do yourself a
BIG favor & dont use any rust converters, soda, POR 15, Ospho or any type of rust "treatments" then coat over them, you're just asking for adhesion problems down the road. I checked on having an AMX media blasted once not too long ago & it was about $800, I imagine a datsun might be a bit less. If it cost $500 it'd be worth every penny, its a lot of work getting rid of all that rust.
Here are 2 autobody forums I recommend you do a lot of reading on - search "rust" on both forum & read, its quite informative.
Good luck & have fun, just remember - if your going to tackle a project like your's you might as well do it right instead of short cutting it which is all those rust converters will do for ya - they just cover it up & save more repairs for you later when its lookin all pretty!
http://www.autobody101.com/forums/http://www.spiuserforum.com/forum.php