Gear Ratio:
Well, if you're looking for more speed, try using the rear end ratio to 3.73 or 3.90, 4.11 gears if gas is no object.
Cylinder Heads:
I would imagine that you have Vortec heads, you could up the air and exhaust inlet to 2.02 and 1.6 and maybe have it ported and polished. I'm not too savvy with porting so others will have to help there. I guess you could also do aluminum cylinder heads.
Exhaust:
Have you tried headers? dual pipes 2.5 or 2.75 with a crossover pipe? High flow muffler? Cut Outs?
Bottom End:
I'm not sure what type of pistons you have at the moment, my guess is the cast iron pistons, you're always go forged or machined but that can be pricey!!! Though if you do that stroke up to 3.75 and have a 383, there are many drawbacks to that but also many pluses.
Top End:
Edelbrock top end kit. was thinking about that myself.
Valvetrain:
Try some roller rockers, it's tempting to up to a 1.6 ratio on a stock cam but it makes it odd because yes you have more lift, but not enough duration. I spoke to a Chevrolet tech and the said the max lift you should run with the press in rocker studs .520, or you could play it safe and while the heads are at the machine shop and have the screw in type. I'm not sure if you want any cam suggestions.
Side notes:
https://www.motortrendondemand.com/show/engine-masters/42026332/
I take my truck on hunting trips, then my Uncle pointed out straight pipes wasn't a good idea.
try looing for engine masters they have a lot of stuff about heads and porting.