Ok.........

As a 40+ year old I will have to gracefully disagree with you about the uh... age of the casting...:o) HAHA

Couple of things I see right off the bat, Firstly, I would not have changed the jets, ESPECIALLY without getting it running first. I know its a minor thing, but its a pet peeve of mine :o) (We go back to aged casting, right). Even if you need a jet change I doubt if its going to be as drastic as you have done, Especially on the secondary side which for your galaxie probably won't need anything done.

Next, If the idle mixture screws when adjusted are not having an effect on the engine RPM then you have something blocked or air is getting in someplace. So here is what I would look for:

Take the carb back apart:

Take out the annular booster, using brake cleaner with a plastic small nozzle spray into the side ports located on the underneath of the booster (where it comes into contact with the carb) they are at the extreme outside edge. IF EVERYTHING IS CLEAN (and please protect yourself since you do not want to get this in your eyes, and do this outside)you should have a nice jet coming out from the small brass tube extending from the booster. It should also come out the air bleeds located above and behind the booster, IF IT DOESN'T THEY ARE CLOGGED. Use a welder tip cleaner to carefully clean.
Next, although it is harder is to spray from each port inside the booster and it should exit from around the big brass tube. Also don't forget the side air bleeds if you have those. Welding tips are again invaluable for this and a primo set of welding tips can be had for under 10.00 from any welding store. REMEMBER YOU ARE CLEANING PASSAGES NOT ENLARGING THEM SO ALWAYS USE THE SMALLEST POSSIBLE.

Once the boosters are clean (and these are always clogged) next take out the power valve and do the same with the passages from the poower valve area to the main booster area. This passage runs from the power valve area through the brass inlets to the main jets pools to the main booster pools (areas where the brass nozzels sit)

Next passage you want to make sure is the accelerator passage which goes from the accelerator pump (small hole below the umbrella seal) through to the middle booster hole (where the hollow screw goes).

Next would be the idle passages, and again a shot of brake cleaner works great, I backshoot through the venturi holes, then through the idle screw holes and then again through the outboard main booster holes.

Lastley would be the discharge holes inside the main venturi area, and the vacuum passages.

Every one of these should flow when using the high pressure of brake cleaner, and flow generously. If they don't then the carb is not clean and they are blocked and are causing your problem. I do all the above, after I have soaked it entirely for a week in carb cleaner, run it through a couple times in my ultrasonic cleaner and used compressed air between both cleanings. AND SOMETIMES I STILL GET CLOGGED PASSAGES.
YOU CANNOT GET THESE CARBS AND PASSAGES TOO CLEAN!!!!!
Nice thing about the brake cleaner is it leaves no residue and is extrememly high pressure and helps dissolve and blow out any last remaining residue.

Good Luck.

Bill White
White Automotive