Like others said $ for $ a 350 will beat a 305 ...just the way it is.
I slightly disagree with UROTU about it not really being differant than any other small block.
The 305 shares the same stroke as 350, but has a much smaller bore. Because of the small bore, the 305 has a few limiting factors. The valves are shrouded by the small bores, some will also argue that you cant use 2.02s in it either , cause they hit the cylinders. I personally dont feel a 305 needs 2.02s anyway...it is only 305 CI after all.
a small displacement small bore engine is also sensitive to over camming & over carbing. I think part of the reason the 305 has a bad rap is cause people tried to apply the same hop up goodies to a 305 as they do 350s...& the 305 ended up being more of a dog than when it was stock.
so, a good stout cam in a 350 is likely to much cam in a 305....the 750 that works on a 350 is gonna make the 305 run like a pig.. etc. etc.
if you build a 305 that will whoop up on some 350s...thats cool...but than the guy with the 350 may have far less money in his engine than you do yours...however, I say go for it if thats what you want to do.
I built a mild 305 a few years ago for my 86 caballero...ran 13.70s with 3.08s....now a 350 with the same money coulda ran 13.00s...so, its your call. John