Thanks, John. Yes, it is nice to be able to make your own decals. A fellow in NZ is selling new ALPS MD-5500's, which might work well for you, since you can avoid the shipping, which makes them about $1,000.00 in the US. http://www.alps-supplies.com/ However, the black markings on that UH-34D should be doable with an inkjet. Just put on about 4 passes of ink if you can. Depends on how well the printer registers. One pass may be good enough for black, The tail rotor caution warning looks odd on that one, too.
The engine bay screens are a matter of trial and error, I guess. Interestingly in the photo of the bird you are doing you can see right through to the sky on the other side. The color depends on your point of view, but either way lower contrast is probably best. I started out with a pretty thin wash and added to it til it looked about right with the gloss OD. I have a Special Hobby CH-37 to do, and I'll probably darken them a bit more, there isn't any light from the other side on them, though what they would have to be right is an engine inside and wire screen. Unlikely in 1/72.
Good luck with it, and thanks again.