My 383 is weak!?

If it's a Performer RPM it will be cast into one of the front intake runners, unless it was ground off for some reason. There is a great article online, Google "383 resto to rad". They built a stock 383, dyno'd it, and then added bolt on parts one by one and gave the results. The version with carb, intake, headers and stock Magnum grind cam might interest you. It made just over 400 HP, and would still work very well with the taller gears you wish to run.