After doing a bit of searching, I am unsure of what the right answer is for an ideal shackle angle. I have read 45-60 degress, is best, but have also seen people setting them to all kinds of different angles. I am doing a solid axle swap right now, with the truck at ride height the shackle is a 20 degree angle. At full droop it doesn't go anywhere near past vertical. Sound about right ?

 

So your saying when all the weight is on it, it is vertical, no angle ?

 

When I jack up my axle, until the frame stops touching the jack stands, the shackles are at 22 degrees. At full droop of the leafs/axle, the shackles do not go past vertical, they are 5-10 degrees away or so. If I am correct, I don't want the shackle to go past vertical at full droop, or I am in trouble.
I have mock up mounts right now, so if the shackles are not okay as is, I can make the rear mounts to compensate for it.

 

All of that work and you have put the shackleon the wrong end.
For best results the shackle should be at the rear of the spring. I fear this set up will cause some severe wobble.
How is the caster?