Fan Belts

Since I now have the triple belt pulley's installed I wanted to put matching belts on the P/S pump. While on my last trip I lost a belt so I decided to grab 2 53" belts from Autozone. When I put them on, one was tighter than the other. I didn't think about, after all it was on there just not as tight as the other. At the next stop I'll retention.
The next stop was 5 miles later, the loose belt took out all three belts.

So when I got home I researched matching belts. I found some for $50 a pair . Then I found Gates belts they claim to be within .01 of each other. I ordered the AX-51 Which is 1/2" x 53. (ordered about 9 months ago) I went to install them today. the belt rides high on the pulley, making it impossible to get on the P/S pulley. A 53 1/2 might work but they don't make one.
At this point I'm at a loss. I put the single belt back on.

Is anyone else running dual belts, what is your source.