I notice that your upper control arm has quite a down slope to the frame. is it like that when the lower control arm is level? maybe have to look into the geometry a little if so. the dimension between upper control arm pivot shaft and lower control arm pivot shaft. otherwise your camber is going to go wonky with a bit of weight added to the truck. the upper arm is shorter than the lower arm so it travels in a shorter arc, that is why the tires lean in at the top when a load is applied. when doing the mock up it is important to have the frame at the rake angle you want when done, levelled side to side, the cross member needs to be levelled side to side using the lower control arm pivot bolts as a guide for your level since the cross member is likely a bit rounded on top (it started life as a flat sheet and was bent to shape then welded then the shafts were drilled and welded in) and not totally in the same plane compared to the pivot shafts, so the level will read incorrectly, and the suspension mocked up at ride height with lower control arms level side to side and fore to aft. upper control arm sometimes has a slight down angle to frame, which helps as weight is applied and tire clearance to fender is a problem, also the upper control arm pivot needs to have a slight down angle at the rear, antidive angle, about 4 deg prolly.I highly recommend a digital level for doing the mock up because the alignment shop will use digital equipment and you want it to drive properly when done.
maybe this will help or you could do some of your own google leg work
https://welderseries.com/tech/tech-s...make-your-own/
https://www.jalopyjournal.com/forum/...ii-deux.70073/
https://www.hotrod.com/articles/inde...nt-suspension/
https://static.speedwaymotors.com/pd...2%20Heidts.pdf
https://www.hotrodplans.com/wp-conte...on-diagram.jpg
http://67-72chevytrucks.com/vboard/s....php?p=7828015
post up some pics from all sides if you feel like it, we would like to see what you have going on there.