The 531 head has a few 'nice' benefits. IIRC it has bigger sodium-filled valves as standard, has larger cooling jackets and passage holes, different combustion chamber shape, better flow, etc.. Turbo addition junkies swear by it because.... ???
Anthony Hyde's page details much more... http://people.physics.anu.edu.au/~amh110/Head/cylinder_head_531_530.htm
Would it better for your 84? That all depends on what your plan is for it. If staying stock, probably not significant. If going for a power rebuild, then probably.
Others will have their thoughts on the #531 head :-)