Just as slow as before mods..

here's what I recommend, in order of complexity;
>does the car roll easily in Neutral?
>does the transmission shift and get all gears (don't care about overdrive right now)
>Proving the flash-stall rpm, and
>proving that your rear gears are actually 3.73s, and
>and yes,as mentioned, make sure the 4bbl is opening all the way by the gas-pedal. This is a two-parter; first the throttles, all 4 of them, have to go vertical; and second, the Secondary air-door has to go vertical when the airspeed gets up.
>a proper compression test, and
>a full ignition timing report. This means your Power-Timing, with the Vacuum advance defeated, from the stall-rpm, to at least 3600 or whenever the Distributor stops advancing; the idle-timing, and sub-stall numbers, are of no importance at this time.

IMO,
no one can help you until ALL of these are known, and
the answers may lead to other questions.
Otherwise we are all just guessing.