I am new to the forum and not for sure how to post a question. Here is my dilemma.. I have a 56 ford customline show car with an almost stock 390 fe. the only thing not stock is dual carbs and high performance coil and dist. setup.. I am going to get carbs adjusted to run right. They are way to rich at this time but can be calibrated down. I can not add anymore hp because there is no room to add headers (have had it looked at by pro custom people). Did 250 hp on dyno (17 inch wheels on rear) and a 325 rear end ratio positrac with 4 speed shifter. Not for sure how much power loss due to the dual carb set up but am looking at how to increase performance on zero to 60 and eight mile runs. At 65 mph in 4th I am tacking 2400 rpm and it will only do 4400 rpm. ( that's borderline to much) If I go to a 6 speed manual shifter and change rear end gears to a 370, will the 6 speed (.63 in 6th compared to 1 to 1 presently in 4th) get me down the road quicker with out hurting my top end or cruising speed?? there are no power adds possible at all because of the header situation.