Much, much better than 305 heads, the 882's have bigger ports and valves and flow more than the 305 heads. The 882's also have a chamber that works with the 350's 4 inch bore. Oh yeah the chamber size is 76 cc's and in standard stock motor form they give 8.5 to one compression ratio.
So how far art you going with the rebuild ?
like giving it a rebore and new pistons,grind or polish the crank, rebuild or replace the rods, definitely a new cam lifters and springs. And if you want more compression with flat top pistons deck the block to get rid of the squish.