Serpentine belt install issues - too tight?

Hey guys, brand new to the site. I inherited a 91 mustang from my grandmother a couple of months ago & the alternator bearing froze up causing the serpentine belt to break this week. I replaced the alternator & now can't get the new serpentine belt to install. It will not go on the last pulley even with the tensioner all the way out. I am using a Gates belt part # K060905 (6PK2295) which I got from O'Reillys. I see conflicting information online if this is the proper belt. My mustang has A/C & I triple checked that the routing was done properly compared to the chart in the engine compartment. Anyone run into this issue? Is this the right belt?

Thanks,
Chris

Yes, I am routing it like the bottom picture. I'll compare the pulley on the alternator to the old one tomorrow. I am using the one that came on the new alternator & thought it would be the same as stock. When installing the belt do you have to put a lot of muscle into it to get it to fit or should it slip right on once the tensioner is out all the way?

Nevermind, got it on this morning. I didn't have the tensioner all the way open (had to wrench from the middle so it didn't hit the airbox). Once that was done I was able to get it around the tensioner pulley.