Strip down the injectors, you've nothing to loose if they don't work after you've finished, the situation hasn't changed!
Google 'diesel injector' and jerk type injector pump' images before you start, to get an idea of where to start.
https://www.youtube.com/watch?v=9THAcQsQM9sPut a large, clean piece of cardboard on the bench and cover that with a length of kitchen paper towel, stolen from her indoors, work in a clean as possible environment. Get a cold one out of the 'fridge, tune the radio to your favorite station and settle in for a couple of hours, take photo's if you don't trust your memory - I take lots!
Count the turns as you unscrew the spring and load the spring up the same amount when you rebuild.
As you strip down keep all the bits in a shallow pan of clean diesel, use clean cloth and wear nitrile gloves, or similar, as Butch said, don't use anything abrasive to clean the gunk off, just acetone, or what ever solvent you have to hand.
Use a fine copper wire (from a stripped down piece of light automotive cable) to clean the injector tip
The tip of the pintle can be reseated, reground, with Jewelers Rouge, a fivers worth off Ebay will last your entire career, about as much as you can get on a pin head mixed with a tiny drop of diesel is enough. don't get it ANYWHERE other than on the tip where you want to reseat it, afterwards clean everything out thoroughly.
Test the injector by connecting it up to the pump before fitting it in the head.
Follow the same routine with the pump, if necessary, it's easy enough to understand how it works, from Youtube and images on the web.
https://www.youtube.com/watch?v=IjXnbFVJKRY I had an Indian injector that was delivered full of what can have only been 'protective' grease, stripping it down, cleaning and reassembling it wasn't difficult, same for the pump.
Have a go!
Cheers Stef