340 vs 383
Like my friend says...there is nothing like a big block...except a big small block.
He had an 800+hp 434 smallblock chevy that would kick the crap out of big blocks at the track all day long. You thought the BB guys were gonna have a heart attack they saw a SB under his hood.
Personally I would stick with the 340 since you're set up for it. I love SBs because I like good handling cars and SPACE in my engine compartment. I would never bother with a BB in an A-body unless it was a 426. To me there is no wow factor unless it's a Hemi.
...but that is me.