I've submitted a question to them about the width etc.
I also see that they have the shackles on the rear of the spring, not the front.
When I did my '55 Nomad straight axle, I no real idea of what I was going to do when mounting everything. I started out with the shackles on the rear, but after a lot of bounching on the frame and I found that the axle moved rearward a LOT when bounched up and down. When I mocked the springs up with the shackles in the front, the axle went up/down pretty much straight. This made me think that the shackles should be in the front; that's what I did.
Most all of the "other" kits for straight axles have the shackles on the front. I may just buy the axle kit from them and do my own sub frame and spring mounting.
I'll see what they have to say about my questions.