The 50004-1 is a Holley 4180 carb. One version of the 4180 was used on Mustangs in '83-'85 or thereabouts. They were calibrated for emissions compliance. The primary metering block different, they made adjusting the idle air/fuel difficult if not impossible w/o going into some amount of work because the doggone mixture adjustment was moved to the carb base and covered to prevent "tampering".
The secondary side wasn't so bad. It could be swapped out for an 1850 type metering block fairly easily.
The carb flowed 600CFM, IIRC and had annular boosters, which is a good thing for responsiveness. The fuel bowls (often found w/ugly vapor vents and hoses) can be swapped out for the center hung bowls.
But generally speaking, these carbs are not in demand. To put it mildly.