First off - WELCOME to Team Camaro
The difference in HP varied over the years for the 305 v.s. the 350 - anywhere from @10 ~45.
The biggest drawback for the 305 has always been its small bore size (3.736") which prevents using larger valve sizes due to the shrouding of the valves and the limited overbore capability of these blocks. These were small CI 2bbl V-8's in all the early confiqurations, used as the base V-8 in almost all applications.
The upsides - if there are any
, is that they shared the same stroke (3.480") and many internal parts from the 350, so replacement stuff is easy to find.
The later production 305 (5.0L) engines with TPI are fairly easy to modify to get a decent street crusing engine - but, you are still money ahead to just start with a 350 and build from there unless you are really interested in moderate HP output and higher fuel milage for a street car.
I've never seen a really highly built 305 in anything other than a LSR vehicle. I can't think of a single performance article specifically trying to build a 305 to have anywhere near the power to CI ratio of a 350 recently* - I'm probably wrong and hopefully someone will respond with the feature article I missed...
(* - I've seen a few 'it what's in the vehicle, so let's run with it' type articles...none of them were all out - how much can we get outta this sucker! )
Hope others that may favor these little mice will chime-in;