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After replacing my water pump, I observed that the fan has a fairly pronounced wobble at idle. It may have always been this way, but the water pump job has caused me to focus on it for the first time.

How much wobble is acceptable? It does smooth out some above idle.

Also, how tight should the drive belt be? I've got the alternator (replaced the generator with 6 Volt pos ground alternator) maxed out as far on the sliding arm as it can get and the belt has perhaps 1" of deflection when pushed in the middle between the water pump pulley and alternator pulley. I can also take and turn the fan by hand and make the pulley slip under the belt relatively easily.

From what I've seen on a number of old-school trucks, belt-driven fans can handle a remarkable degree of wobble before they get problematic. That said, there's potential for a broken-off blade to punch through the radiator or dent the hood, so the stakes are high. If it's a case of bent blades (versus poorly-distributed weight), you can attach something to the back of the radiator as a distance marker to see how far off each fan blade is. Set the marker to a blade of your choice, then rotate each blade to it and see how far off they are. Blades can then be carefully hand-bent to match the marker. Not as good as professional balancing, but it should reduce the wobble.

According to 26th-series Packard manuals, the belt should be tight enough to rotate the engine when rotating the generator or water pump. To my mind, that seems aggressive, especially with a dry or partially-glazed belt. With a brand-new belt, sure, but realistically, V-belts are not especially sensitive to tension. If you're at the limit of the tensioner arm, I would definitely grab a shorter belt (1-2in shorter should do it), just so you have room to add tension as the belt stretches. Hard to gauge if that 1in of deflection is "about right" without knowing more about the level of force applied.

Thank you,Lex, that is very helpful!

The wobble will cause accelerated water pump bearing wear.

I would lay the thing on a flat surface and improve the situation.

Good call. Will do that!