I realize you've likely already made your decision on the tripod by now, but I have a Slik Pro 330 EZ and also a Slik Pro 340 EZ (the smaller version of the 330), and I have liked them both very well. They have a single-handle, pivot head on them that is great for glassing on a grid. The smaller version collapses down and fits in my pack very nicely, and is also functional from a standing position (although it isn't as sturdy all the way up as the 330). They are smooth, high-quality tripods that will last for years (and mine have). You can get either of them for less than $120. They also make carbon fiber versions if you want something lighter, but those run closer to $300. I've compared them to the Vortex tripods, and I think the Slik is a better tripod for about the same money. The motions are more smooth, and everything is a little tighter than the Vortex.
If you are mostly going to be close to the truck or horse, I would probably go with the bigger one as it is more sturdy in standing positions, but the smaller one is more versatile if you're going to backpack with it.
As to the ability to hold a Kowa spotter, I think they would both do well. I used both of my Slik tripods with a Zen Ray 82mm scope for several years without any trouble. The Zen Ray weighs 64oz., and I think the Kowa weighs about 49oz., so you should be just fine with either tripod.
Good luck.
