will 91 k5 bumpers fit 80 k10?
 

buddy at work has some nice bumpers of his 91 blazer that he said i could have for the '80. will they bolt up?

No.

I believe the brackets are different, as are the frame mounting points. The bumpers themselves also look different, the 81+ bumpers are more squared off as opposed to the 73-80 more rounded bumpers...at least the fronts anyhow.

Not a bolt on but it can be done. The front of the 90 will have some brackets bolted on the top of frame horn. Little metal work on the 80 frame horns and you can bolt those brackets on.

You need to do this for the front:
http://www.captkaoscustoms.com/images/bumpertrim1.jpg
http://www.captkaoscustoms.com/images/modifiedhorns.jpg

so you just have to trim the horns some and everything will bolt up? does the rear bolt right up?

From memory it was 2.5" from the line to the far most point of the frame. If you have the 81-87 bracket, it will give you a guide to cut at.

Yep, you do have to have the front 81-87 brackets though. The rear should be the same, I don't think the bumper mounts points changed, just the look of the rear bumper.