Hmm.. Let's see.. First.. The UnaBlock is kind of a stretched U design. Water enters, travels an inch to the right, and exits. So it's a very flat bottommed U.
It is aluminum, and I haven't made a direct comparison of it to a Maze2 yet because I have it running on a closed loop system that is a royal PITA to fill/bleed. From what I can tell, it's performing wonderfully. AND I have it setup with a BlackIce classic.. All copper radiator, no worries because I have water wetter in the water to eliminate corrosion. I did recommend Royal Purple in my buyers guide, so they won't have a problem either, if they don't take shortcuts.
I recommend the Via Aqua pump, because it has a better reputation than the Rio, and because it has a higher flow rate. I have my UnaBlock setup with a Rio pump, and with that highly restrictive radiator, the water comes out in a trickle. (Still does the job though..
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As for buying a heater core, 9 out of 10 mechanics are assholes, but auto parts stores are auto parts stores. Most of them are part of national chains, go to one of the national chains, and start asking there. Fedco's site lists everything way over the price it should be. As a last resort, Carparts.com might be able to hook you up, I know they used to list the heater for a '77 Ford E100 Van at like $13.. But they were out of stock, and they'd usually give you a call and try and talk you into something else.. Still a good way to get a good deal, ask them to give you any other heater core they have, just do it at the same $13 price.
As for cases, name brand = not budget. I usually go into the cheapest computer store I can drive to (about 35-40 miles from my house), and buy the cheapest case they have. Last I heard, that was about $23. heh. Saves shipping, and it is functionally as useful as any name brand case. The only thing you might want to do is buy a decent power supply for it, seeing as how they always come with a deer.
How is Tygon with UV? Zoson says his dye-lite isn't lighting up inside the Tygon as well as it did in his silicone tubing. But then, he is using Blue dye-lite, so that probably has alot to do with it.
Different size fittings.. Well, if you run silicone or tygon, it won't be an issue. But being a budget setup, you'll probably use vinyl. Like I said in the article, you'll just have to be inventive. For the radiator, what I did was go to the hardward store, and pick up a pair of 3/8" hose barbs, and pick up some JB Weld (it's an epoxy with steel in it), and glue those hose barbs onto the ends of the tubes coming from the radiator. Worked great.
Hmm, I think that's all the questions..
Hope that helps.