Looking for the best replacement springs to return my 69 340 Swinger 4 speed to original height.
Car is laying down about 1.5"- 2" in the rear.

I heard Eaton springs were pretty nice but I have no experience with them. They give you a option to choose the ride height. https://www.eatondetroitspring.com/

I've bought from ESPO - aka Springs 'n Things - a few times and have been happy with them even years later.
They also have stock height, +1" & +2" - I generally go with +1".

automatic weight transfer ... My 69 Dart 383 car is like that , other than having to jack it up by the bumper to get the F70-14 off what's not to love ?

I have Espos I bought for my 69 Superbee , but have yet to install them.

i've used espo 6 leaf springs on numerous cars and really liked them.. on our current 70 dard we used the eaton springs.. wanted something with more spring rate so we went with a set for a 383 dart. real happy with those too. the eatons are more expensive.

the woman at espo knows here stuff ans they have great customer service. https://www.springsnthings.com/

if you want the eaton then give pete a call @ https://bergmanautocraft.com/ and he will set ya up with what you need.

X3 been using Laura at ESPO ESPO LINKY for over 20 years, never a problem of any kind

If not broke see if you have a spring shop Get then rearched and add a leaf if you like a nic stiff ride Had them done on my kids 62 300 They were on 15 years when he sold it and still running today 8 years later.Was raced and had thousands of miles Lots bette then the stuff you get today

ESPO is top Notch ! I paid big money for a set from Eaton and they laid down in no time . I bought a set from Espo for much less , and they have been on for more years than I can count. Still perfect !

You wouldn't know it from their website that ESPO sell leaf springs.

A reach doesn't last without adding an additional leaf for support
I've had several sets rebuilt and done this way.
On my 78 fury 2 door, I pulled them, had them reached and it didn't last a season
They were sagged as bad (or worse) than they started out with. I ended up band aiding it for a few cruising seasons with air shocks and last year I finally ordered a set of new ones from general KC spring.
In 78 that car could have come with a 4 leaf, a 5 leaf or a 6 leaf spring. Mine was originally a 4 leaf pack, I went with a 5 leaf and like how it rides now. I went back with standard shocks and got rid of the air shocks.
I've had mixed results with adding a leaf. On my diplomats an extra leaf improved the ride, as it did on my 94 Dakota (reg cab/short bed) but on my 96 Dakota (4wd, cab and 1/2) and especially on my 01 Durango an extra leaf made those like lumber wagons. The Durango though was all over the road, wishy washy no matter what else I'd done prior to the new springs, and the new springs cured that.

The cheapest and most positive fix is to use the Hellwig helper springs. Under $100, easy install, adjust to your preference in a matter of minutes, last just about forever, etc. There is a recent thread on this.

Way back when (about 15-18yrs ago now !!) I bought a set of MP super stock B body springs for the 70 Sport Satellite - they only lasted about a year, before they started to sag and then get to point they were arching other way !!! Not sure if Mopar Performance springs have gotten better since then, but I took the original springs in for a re-arch and add a spring . . . have been on the car now for 8 or 9 years, and no sag at all.