grinding off truck motor mount bosses?

Crap. Now im just going with hipo manifolds, but eventually with tti shorties. I so don't want to paint that block, install it and then find they don't work a year from now.

As mentioned it would probably be best to wait until you see where what you put on it interferes with if anything.
I have Headman long tubes and if we refer to your picture I had to trim off about half of the one pad closest to the head.

It wasn't bad to do in the car though with a 4" grinder with a cutoff wheel on it.

Here's how I had to cut mine, as the corner with the X was where the headers hit.

IMG_20170620_161502916.jpg