Don't check the box, check your carbs. If they have accelerator pumps in the front & rear bowls they're double pumpers.

Considering all options I may try to sell the 450's and get the vacuum 600's. What's the best one to get given my circumstances?

Gotcha alright didn't even open the boxes yet haha.

Looks like it's a single then. Yeah I guess I best start going the vacuum route then. Thank you saved me from a lot of headache later haha.

Your 450 carbs are made for multiple carb applications but they're not a good choice with your convertor, car weight and gears. A better choice would be an 1850 600 as listed above.

Just got the 2 Holley vacuum 600's for a nice price. Thanks everyone for your input!

Start familiarizing yourself with holley tuning. I wouldn't expect to plop them on and have them run perfect right out of the box.

Go to this site and get these guys to help you.

Amazing what they will tell you.

http://racingfuelsystems.myfunforum.org/

What kinda power you think I'd get out of this set up? I was looking and it seems like it's around 500 horse but not sure, anyone have a better idea?

Thanks will do!

You won't know how much power the motor will make until you run it I have made 430 HP with a mild 440 stock 446 C.I. iron headed pump gas street motor with a six pack on a DTS engine dyno. I have also made 535 HP with a 451 C.I. 440( .055 over bore) motor with ported big valve pump gas iron heads and a lot bigger solid lifter camshaft with a single 850 Holey D.P. carb.
Cam timing, jetting, exhaust system and a bunch of other things end up helping or hurting how much power a motor can make
I've seen 80 HP loss and gain by changing the cam timing(going from 5 degrees advanced to two degrees retarded) on a engine dyno test
The 4.10 gears in that car will make you wonder were all the power came from
Drive it first with the 2.76 and then the 4.10

Not to mention how much more of a hassle it will be to tune the Holleys compared to a set of Edelbrocks.

The Holleys will have to be removed and the fuel drained to get the bowls off for jet and metering plate changes.
Edelbrock metering rods are swapped easy enough and will only need the top off for jet changes.

If those are stock heads on there, I don't think you'll be far over 400hp. 430 sounds about right with good carb tuning, good cam and ignition timing.

I'm not sure all I know is they're ported and polished. Didn't the factory high performance 440s make 410 at the flywheel? Seems like all this for 20 more horse is kinda low haha.

Edit: Removed my valve cover the other day and it looks like it's the 346 head.

If the heads would really be killing it that much anyone have any suggestions for a set of heads that would work well with my build? With in a mildly reasonable price if possible haha,
The number of 500 ponies is where I'd like to ideally be at.

Start with what you got and then see if your happy or not If not, fix it
Every body wants what they think they want, until they find out what they thought was good was too much
Ask any Hellcat driver

The Weiand tunnel ram allows you to mount the carbs sideways to facilitate bowl removal.

Back in the 70's I ran a 440 in a 64 Fury wagon with a tunnel ram with 2 - 750 double pumper Holley carbs, I did run a 4 speed with 4.88 gears. I didn't have a problem on the street or the track but one thing I do remember is spark plugs only lasted a week and twisted off a lot of u-joints.

Good advice cab, definitely run what you brung before tearing it apart.

Furious, when someone says heads have been ported and polished, that means nothing unless they provide a flow sheet. Enough flow for 500hp usually involves considerably porting, and oversized valves, or aftermarket heads.

Gotcha I'll just have to dyno it once it's all said and done. I don't know what was done and I don't think I can unless I start tearing things apart. The only facts I have is that it's got the the Weiand triple Bug catcher air scoop, 1987-Weiand high rise Tunnel Ram, Dual 600 Vacuum Holleys, 21-225-4 Comp Cam, 1 3/4 headers to 3 in collector, 3 in H pipe exhaust to flowmaster super 10, compression probably around 9:1 assuming stock, and evidence that head work was done on 346 1971 heads (double springs and the port and polish, but as stated no flow sheet.) we'll have to wait and see how she takes it.