Go with electronic ignition from a newer LUV/Isuzu motor (81 and up) for a nice stable fat spark. Check out the info section of luvtruck.com for a list of parts to get and how to put them in.
I like plain Bosch Platinum plugs, split fire and all those other multi prong plugs I've never heard a whole lot of good about. You could go with Denso Iridium plugs too, though they are spendy
The wires, well just new wires is a step up for most luvs
Cam:
http://www.deltacam.com offers reground cams that increase lift and duration.
Header: pacesetter makes one, you can also sometimes find other brands (Thorley, Hooker) on ebay though I don't think you can still get them new off the shelf.
Carb: Weber makes two. A 32/36 progressive and a 38 syncronous. The 38 is overkill unless you have some other mods to go with like the header and cam. If you can make an adapter plate you could fit a lot of different carbs on there, but the webers are about all you can find on the shelf with an adapter already made. Check out
http://www.carbs.net for pricing.
A glasspack will be loud, I ran one on my 77 for quite a while and it was obnoxiously loud. If you couple one with a split resonator tip you might tone it down enough to keep the law off your back though.
You could add in something like an MSD ignition system for better spark, though the gains will probably be pretty minimal. There are a few dual sidedraft carb manifolds out there, but finding one usually means shipping it from Australia. Personally, I gave up trying to squeeze more out of the 1.8L luv motor and have started gathering parts to put in a 2.6L Isuzu motor into my truck. As the V8 guys like to say, there is no replacement for displacement.