Modifying the install tool from post #25 didn't work. I was able to get the NAPA 7390 belt on by taking the arm off the top and grunting strenuously, but it was a real struggle. Turns out, in addition to the arm touching the hose, the body of the alternator is in significant contact. The previous hose was lighter duty allowing it to compress enough. So, the answer is not putting a curve in the arm to relieve contact with the hose. I need to lengthen the slot and use a 7395. But there's only so much room before the alternator hits the bulkhead.
In the meantime, the belt now has enough tension to get the power and pumping I feel it needs. So I can punt that project down the road. When I get to it, if I'm smart, I'll follow Christian's recommendation.
* I just noticed the asymmetrical fan on the alternator. That's weird.