I've always stayed away from anything electric or pnuematic when removing gasket. Plenty of people use them with good result, so it can be done. My mentality is anything that makes a job go faster also has the potential to make things go wrong faster. A non-abrasive disk is going to take one helluva long time to start machining steel, but there is always the potential. I'd rather use a little more elbow grease and rest easy at night. Keep in mind you are only trying to remove the gasket itself. Don't worry about and stains left on the block/head surface. Trying to sand/polish stains out is a surefire way to end up with variance along the mating surface.
Yes, I'd recomend removing the injectors prior to head removal. That sum***** is heavy (150lb IIRC) so it would be a shame to ruin injectors while wresting it off the engine. Didn't use any special tool to remove injectors, just a little love from a pry bar. There is an injector puller, but they are spendy. Would also be a good time to inspect injector cups/o-rings for any signs of failure.
There is a specialty tool for removing heads. Utilizes the 4 centermost threaded rocker arm retainer holes, and attatches to a engine hoist. Depending on available resources, you could easily make one. Like i said before, these heads are heavy. Trying to wrestle one onto the block with the engine in the truck is a task without some sort of lifting mechanism.
$800 in funny money eh?
Have you looked into the Tymar intakes? Run around $150 last time I checked. Could also go for a DIY 6637 intake. I'm sure there are writeups on that here somewhere.
For a HPOP, Terminator Engineering's T500 should do everything you could ask of it. $460 shipped to your door I believe.
Is your fuel bowl leaking? Diesel 0-rings sells a complete rebuild kit for them. With the price of fuel these days, it should pay itself off in a fillup or two.
If your running the stock downpipe, I'd say upgrading to a 3" one (if not a full exhaust) should be at the top of your list. They are relatively cheap and easy to do. You'll want to remove the stock DP if you're removing the passenger side head anyways.