Need carb and/or timing help

If you have ruled out vacuum leaks a big drop in rpm between neutral an drive is an indication of not enough initial timing. If you have a cam with a lot of duration 18 or more initial is not uncommon. Like previously mentioned you will have to limit the total in the distributor to keep it in the 34-36 range that sb open chamber heads like. This is where an aftermarket distributor like the mopar performance unit that has adjustable mechanical advance will makes tuning easy.