Header's would help.
Your's is probably the 250 with the integrated head, so swapping carbs won't help much. You will still have the same poorly designed intake. You could get an older separate head with the separate intake. Then add headers, intake and carb, which will liven it up alot.
www.inliners.org and
www.stovebolt.com are the best 6 banger sources I know of.
Best bet for the $$$ is put in a 350...6 cycl;nder parts are much more expensive when your hopping up an engine.