At this point, it has nothing to do with the tranny angle. What if it was a four link rear end?? What is the angle of that?? You don't know 'cause the links could be set at any adjustment. Four link brackets could be welded in at any angle. Same with the spring perches. They could be welded in at a 90 degree angle to horizontal. That would be fine if you had a weird spring set up that way. Where stuff is welded doesn't matter until you have an application.
Now, if you are doing a comparison to what you already have in your truck, well then yeah, the spring perches are odd. What angle is needed for a 1975 3/4 ton Chevy van?? Who knows?? Maybe that 12 degress at level is proper for that 1975 van? It means nothing until you have something to put it in.
As far as what it came out of, could be anything! I mean, it's like, "All the bolts in my garage are 1" long and I found an 1 1/4" long bolt. Anybody know the application?" Could be anything! But as far as comparing it to what you have in your garage, at the very least, we can eliminate that kind of vehicle.
Maybe it came off of a monster truck? Well, that's what grinders are for. To make it fit to what you want it to.
