GDP -
Glacier Diesel Power
If you go to the PacBrake website in their technical information you will find the installation instructions. The compressor mounts using the outboard/front bolt of the intake horn for mounting. If you are installing it on a stock truck with no modded intake horn it will fit just fine, it also fits just fine with the GDP horn, it will not fit just fine with the other types of aftermarket intake horns.
I mentioned that I had the GDP intake horn and that it mounted fine with it just in case you (or someone else) was curious about it fitting with that horn.
There is also a post here on this site about the GDP intake horn and it having been dyno'd, excellent information about the horn and it's functioning on our trucks.
CD