Well then I will build one out of a couple pieces of 90 and ready rod as you did! Do you bolt the spreader to the bearing cap bolt holes?! Probly not seems like a sensitive place
And I think I'll reuse as much of the stock thick shims as possible, it sounds like a nightmare from your description with all the .002s an such
No definitely not the bearing caps that'd probably be a bit of a disaster, it bolts to the cover bolt holes in the housing, 2 on each side. It doesn't spread nearly as much as a real case spreader, but I got I think 5-10 mils out of it which is enough to work some good shim stacks in.
The thing is you're going to have to tweak the shims to within a few thou, so you're going to end up with a few very thin corrections. The people who put the shim kits together seem slightly mathematically challenged, but for the most part get it right, really they should send out 1, 2, 4, 8, 16, 32, 64, ... mil then you can get any thickness you want to within 1 mil, with as few thin shims as possible, with a kit that contains the fewest total number of shims.
The factory presumably has a set of every single shim thickness (60, 61, 62, 63, 64, 65, ... mil) which would be tremendously cost prohibitive to have in a home kit, but for a factory the cost of stocking all the parts is nothing and it allows them to have a single shim per side for easy installation and servicing.