Do yourself a favor and buy a Holley Street Demon 625cfm. It has the most modern metering circuits and will bolt to either squarebore or spreadbore intakes. Get the one with the space age plastic bowl, will keep the fuel cooler.

The numbers you gave us do not say much about the carb you currently have. The number that really matters is stamped into the front of the airhorn/choke tower. It will be something like "LIST 1850-6"
The next row down is the Holley date code. It isn't really important as the list number tells all.
Sometimes the word "list" is replaced by a capitol "R".

If it is a Ford carb it will have the ford part number, if it is a chevy carb it will have a chevy part number, both usually have some more Holley numbers, sometimes list and sometimes not.

Everything about the carb can be found in the Holley Carb Numerical Index. EXCEPT I recently looked at the numerical Index on the Holley site and found that they are leaving out part numbers for items they don't currently sell. We are lucky that there are still copies of earlier numerical Listings available on the internet. For example, at one point in the '70s Holley began to sell carbs that were emissions legal. These carbs used Holley higher precision jets, recognized by three digits. An example would be a jet marked 602. It's a close tolerance 60 jet.
The old Numerical Listing contained the number for the jet for a particular carb. The new Numerical Listing has "NS" in that spot. If you have a box of jets and are trying to sort out the ones for your particular 6619 or 6919 or other emissions carbs, you cannot using the new Numerical Listing.

May mean little to some of you, it means a lot to me.

R.