So I have the spider gears out and there are shims in the case halves. Do these come out when installing a Detroit? I left them in at first and when I put the two halves together they don't seem to mate together 100%. I tried using the impact to squeeze them together, but there seems to be a small gap on one side. I have a set of directions from here http://chevy.off-road.com/chevy/article/articleDetail.jsp?id=275119
but it says nothing about this. Also the Pirate 14 Bible says nothing about this as well. THanks.

IIRC the instructions say to remove all shims. Read through them.

Ditch the shims (or washers, whatever you want to call them).

10-4, I took them out and everything went back just fine. Thanks again!