Well, it appears we may well have been right. Went to the vet this am, he did blood work and a good "once over". Still no fever, blood work was quite normal - with white cells just slightly elevated. No nasal drainage, but swelling increasing in throat latch area.
Vet's thought was that we are just at the beginning stages. Most likely Strangles, perhaps a version of Pigeon Fever. I've isolated him and grabbed a quick vaccine for my other two, although it may be too late if they've been exposed.
As for now, he's on a bit of Banamine and only time will tell!
Gotta love a good, nasty case of Strangles.... NOT! Although Strangles isn't fun, it's a whole lot better than something that's life-threatening!
Thanks for your input and sluething skills!