As someone who has raced a Datsun 1200 for the last 25 years I will third the opinion that they are a good car. You can find everything you want to know at datsun1200.com to be truly C-sedan legal you would need to stick with the A12 engine but VARA does have the GTL class which will allow you to run an A15. The cars advantage is light weight, even with my overbuilt tarmac rally spec cage it is 1680 lbs. I have a fairly low spec tune on the A15 putting out a little over 100 hp at the real wheels versus a full race engine putting out 150hp.
Tom