Correct part number is 34175. Check first that the part number on the box and the actual part is the correct part number.
2000 GM 6.5 AC ByPass.png
Reason being, I used to work at an Auto Zone and I saw people returning all the time because some idiot didn't pay attention or listen to them and gave them the wrong part, or sometimes we actually had received parts for resale, only to find out the wrong part was in the box. Something that usually wasn't discovered until after a pissed-off customer returned. We certainly didn't open every box to verify the correct part was in the box. So verify it is the correct part first.
If the part is the correct one, three things...
One, most of these bypass pulleys will be designed to either bolt to the stock compressor bracket, or replace it altogether. So check to make sure it is not designed to replace the existing bracket. You may have to remove the bracket along with the compressor and bolt the bypass pulley in the bracket's place to make it work as intended. It's also possible this part is designed to fit multiple applications and may have bolt holes in the bracket that aren't used on your application.
Second, you may also find that a shorter belt may be required, if the positioning and bypass pulley are different than the compressor.
Third, it is possible you may be thinking it bolts on a certain way, which may not be the way it has to. I've had that happen a few times and it took a little while of messing with it to realize I was trying to put it on wrong.
If all else fails, I would just leave the compressor in place. The pressure cutout switches will not allow the clutch to engage, so your primary goal is effectively already accomplished. I would disconnect the clutch just to make sure.
I get that some might not care for A/C -- however, it seems a little extreme to gut it down to removing even the compressor just because you can. No offense, just my $0.02. But to each their own.