Technical Straight axle set up questions

This question goes out to all the guys running "straight" or dropped beam axles , I've been gathering parts to do this swap on my Henry J . ( I've done a search and read all 125+ posts and links ,lots of good info ),the pieces are 1937 chevy stock ( factory 4" drop ) beam 1948-1953 truck spindles 015 over king pins and bushings (machine shop installed ) speedy disk brake kit , and 31" 6 leave springs, and mounting hardware package, I have removed the third and fifth leaf of the springs to hopefully soften things a little , here is the question, i want to set this up with the shackles in the front, which would mean in the lifted( unloaded on acceleration / no weight) position the axle / wheels will be at their furthest rearward position , as the car settles ( cruise speed or braking) they will travel towards the front somewhat ,( arc from rear pivot point) . Now the big question... I want to set this up with the wheels slightly forward (ie altered ) about 2" at ride height , should I set the rear pivots to position the axle at 1 1/2" further forward of the stock wheelbase , with no load, ?? does any one have any idea how much further forward the wheels/axle will travel when loaded / hitting bumps /bouncing /landing , the car will be smallblock(355) powered with a slight 3-6" engine set back auto 2500 stall and 411 rear won't be nosebleed high but it will leap,Thanks guys for reading and any light you can shed ,this place is an awesome commonwealth of knowledge,
Hoping to get back on my build soon, Regards JT

 

Too many possibilities without all of the weight on the axle. As a rule of thumb, if your steering is in front of the axle put the shackle on the front spring attachment point, other way with steering behind the axle.

 

I wouldn't think the front spring eye would move more than 3/4 to an inch and half of that gain would be in front of the axle, where it won't affect the wheelbase. Here's a pic of mine, even though I'm a long ways from knowing if it works or not.

 

Thanks guys,
Blue , looks like a nice project , love those orphan "J"s ,have you had an engine in your J since the axle install? If so how much did it settle from the " unloaded " height ? How many leaves are your springs.? Where did you source your front shackles from? The ones I got from speedy seem short
( 1 1/2" center to center ,like for a model "A") sorry for a million questions, (and crappy cell phone pics.) again Thanks , JT

 

I bought my car as a project with the axle tacked to the stock frame. I built the new frame stub to raise the mounting points so it didn't sit as "nose high" as it did before. As it sits now, I have 2 leaves removed per side. I think I took out the shortest and the 3rd shortest so I have 3 per side now. I think the shackles might be trailer parts. I have had an engine/tranny mocked up and I think it settled it 1" to 1 1/2" but I don't remember if I had the leaves pulled yet then.

Blue

 

When I did my 55, I tacked the front shackle mounts on the chassis. I left it like that while I installed the motor, trans, radiator support etc. In the period of a couple months the springs did settle and I wound up moving them 3/4" further forward from where I had them tacked. Seven years later, the shackles are still at the correct angle. Tack them in place and go on the another part of the build. Takes the "guess" right out of it.

 

Blue , thanks again, I will check out shackles for trailers , sounds like a good source , good luck on your project.
Baron, thank you too for the input , I've had the eng/ trans mocked for floor trimming and checking header fitment, you are right, the best plan is tack/ clamp things together and load the weight back in to take the guess out , I keep forgetting there no absolutes as we re-engineer / re purpose these old gals .... Thanks guys very much for your input / experience. JT