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I run 2.5 western spindles with my stock 15's on my 73 blazer 2wd with no problems. IDK about the shocks. I have Beltech's drop shocks with the spindles and 1.5 coils cut on stock springs. That's about 3" on the springs and I had to trim the bumpstops. I have a big block though so it may be different for you.Where did you get the kit?
There is an aftermarket mount you can use for severely dropped trucks.http://www.earlyclassic.com/fullImage.aspx?productId=168&productOption=02-5402If you are using drop spindles, you can use stock shocks the geometry didn't change.I usually cut the bumpstop down if I am just mildly dropped, spindles wouldn't need to be cut as again nothing really changed.
If you are running 2.5 spings, you need to just cut it off and bolt a bumpstop to the lower control arm.. That shorter bumpstop isn't going to help with 2.5" springs.