If it's just the short block, it doesn't really matter to much as long as it donesn't have dish pistons (lowers compression). The early "general duty" 305's had those and run around 8.6:1 compression = You want to get a 305 short block with the flat tops, which will be around 9.3:1 compression ratio with a stock head gasket and a 58cc chamber (stock 305 head chamber volume)

If it includes the heads, the desired head casting number will end in 416 for an '82-'84 H.O., and also for '85-'86 TPI. '87+ TPI 305's will be 087 and are the same head as the 416, just with a revised intake bolt pattern/angle. Don't go after any other 305 heads as they are all junk. If you happen to find a set of the 113 casting aluminum 'vette heads, they also have a 58 cc chamber and carry larger 1.94/1.50 valves and flow very well for a stock set of heads.