As far as the resonating elements being perfectly straight, it's not an absolute requirement obviously but that doesn't mean you can't do your best to get them as straight as possible. You can also make one of these from electrical wire, typically 10 or 12 gauge is best (that's what you'd find inside the walls of your home or apartment feeding all the AC sockets), 10 gauge being just a bit thicker overall and almost a perfect fit for the holes in the SO-239 chassis mount. My first homebrew multiband I built wasn't even soldered at all: I just put a tiny bend in the ends of the coat hangers (like about 3/16" of an inch from one end) and bent it back enough so that the element literally hung (hangers being hung, go figure) from the corners of the SO-239 mount, and then put the main element into the top of the mount with a tiny piece of aluminum foil wrapped on the end to make it a slightly "tighter" fit.
The PL-259 plug that I used was a screw on connector (meaning the RG-58u that I had laying around was attached to it just by stripping off the wrapping and then inserting it to the base of the PL-259 and screwing it into position on the cable - no solder required. The other end of the RG-58u was yet another screw on connector for the male BNC which then attached to the MCX-BNC pigtail going into the SDR stick.
Worked fine for months, and even when I "improved" my build with solder and screws and spade lugs, it worked pretty much exactly the same meaning that just because it was done "proper" the second time around didn't mean I suddenly got a +6 dB increase in signal strength or anything: the "proper" one worked and still works exactly the same as the un-soldered thrown together first attempt (which I still have here as well).
As far as specific 800 MHz coverage, that's the beauty of these oh-so-simple wonders: you can just get another SO-239 chassis mount and make one cut for 800 MHz specifically, it's not like you're going to have to spend a huge sum of money for these things, and if you do end up making one cut just to 800 MHz (I myself have one cut for 450 MHz and another one for 890 because I do monitor the traditional 850-860 MHz as well as 935-940 MHz so 890 sits smack in the middle for handling both ranges effectively) you're ahead of the game definitely.
I'll be making yet another one here this weekend cut to about 770 MHz since we'll be getting some more service in that area here in Las Vegas soon enough - our Metro PD will be starting up a new P25 Phase II system soon to replace the abomination they've had for 2+ years now known as OpenSky (what a failure that's been overall) and another system will be added as well, also P25 Phase II which is a big county-wide multi-system thing. Should prove interesting...
Now if only DSD+ could do P25 Phase II I'd be getting somewhere.
But that's the beauty of these homebrew antennas: they're simple and cheap and do offer damned good performance more often than not - and don't leave the homebrew OCFD out either, it's still relatively cheap to make from some copper pipe (or even plain old electrical wire if needed, for a rolled-up portable version) that may work well for you in your area.