Replacing fan belts on a Ford 223

The belt that operates the alternator on my Thiokol 601 with a Ford 223 industrial broke. This motor has two belts, the outer belt to the water pump. the inner to the alternator. Since I have to remove the water pump belt to install the alternator pump I've decided I might as well replace both. I can do the alternator belt fairly easy, but the water pump belt has me stumped. As you can imagine I'm working in very tight quarters. How do I relieve tension on the water pump belt? I can't see a tensioner. I tried to find a diagram online but they are all for modern serpentine belts.

my foggy memory thinks you loosen up the water pump mounting bolts from behind and the water pump will slide a little to the side ! Stupid idea and prone to leaks ! Someone will correct me if this is wrong .
ST-2018

Different engine but - on my 170 engine the bolts that hold the fan on also hold the pulley on. Remove them, and you can pull the pulley off the water pump shaft.

Any chance you can run a single belt around the water pump, alternator, and main crack. Then you can tension the belt via the alternator without having to mess with the water pump. If you have double belt pulleys on all three, you can put two belts on.

For future reference, The fan is mounted on a bracket. There are two bolts that when loosened allow the bracket to slide up and down.