I just put on a Airtex AW4114 on my 2000 7.3 from rockauto.com ($78 + shipping). It came with the cast elbow and o-rings, except can't remember if it had the t-stat o-ring or not. Quality looked top notch to me. Replacement took 4 hours with a helper and a 1/4" drive air ratchet. Only tough parts were getting the darn temp sending unit clip off and one of the catch tank cage nuts spun on us, could probably take off about 45 minutes without those problems.
For what it's worth, I have seen posts of 15,000 (amazon review) and 100,000+ mile Airtex installs that are OK. At $223 for a Motorcraft you could buy 2 Airtex (but still a PITA to change it again).
I bought a new Motorcraft t-stat housing from them also, I wouldn't mess around and try to use the old if it is rusted at all. Also got new rad hoses and from Advance, 195 deg Stant t-stat.
You can rent the fan pulley holding tool from O'Reilly's for free, and if you don't have the 1-7/8" wrench for the big nut, you can use a pipe wrench...mine looked rusty but it wasn't really very tight and the pipe wrench did not hurt the nut at all. Have a helper hold the fan pulley from the side with the tool.
In my opinion, use the Permatex non-hardening gasket sealer in the white tube to hold the big main o-ring in place, put a little bit at the corners and on the long parts...silicone may start to harden.
Here a link to a waterpump how to article: Ford Super Duty Water Pump Replacement Procedure | Superdutypsd.com
Here is a link to Powerstroke Help youtube videos on 7.3 waterpump:
Sorry if more than you needed to know.