Rear ended moving around, need some tips.

You don't think you can find a spring bolt with the correct threads and a larger pin (the part that goes into the spring pad). If they don't make the spring bolt that you need then you could get a longer spring bolt (I know they make them in various lengths) and slide a spacer, something like this:
5/16" ID X 1" OD X 7/8" TALL STEEL STANDOFF, SPACER , SLEEVE , BUSHING (4pcs) | eBay

onto the extra long spring bolt so that the spacer fits up under the head of the bolt, then you'll have a larger diameter pin to stick up into the spring pad using the correct diameter threaded bolt. There's usually a lot of space between the spring pad and the axle tube but it the old pin sticks up too much you can trim it down some because the spacer will now center the bolt in the spring pad hole.

Treblig