After re-reading your initial post, I believe you need a bigger carb. 1406 sounds a little small for your mods. I would think in the area of 650-700 cfm might work better. Also, the shorty headers don't scavenge the exhaust as well as long tubes. Have you experimented with any spacers under the carb?
4 hole or open plenum? Not much room for that under the hood of an S-10 huh?