Jim,
I found a bit of a Pandora's box when researching this a couple years ago. There are some resources out there, but they seem to conflict.
Horler (Original Sprite & Midget) has photos on page 100, 102, and 103 of under bonnet decals on an original '73 Midget. This was my primary source. Both the MG plate and the patent plate had already been afixed to my valve cover when I bought the car; I did not alter them.
The Coopers decals on the air filter cans appear to be black in the very small engine compartment photo in the original dealer brochure (10/72)for the '73 model; you can view it here (center/bottom):
https://www.raysmg.com/Web Images/Edited/MG/Advertising/Brochures/MarkIII/10-72/page3.jpg
If you look closely, you can also see what appears to be the blue sticker on the valve cover. I did not use one.
The Coopers decals I could locate came in blue, so that is what I used. Also, I used a photo that was incorrect in their orientation and duplicated the error on my car. The decal should be placed so that it can be read from outside the car, ie., facing the engine from the driver's side fender. Mine are pointed inward. I have that on a list to correct when I pull the cans off for respraying. You might want to be careful not to use a super glossy black powder coat on them...looks good, but not correct.
The two heater stickers are relatively easy as are the firewall warning sticker (just visible at the top/left in the photo below) and the radiator warning (just visible at the bottom/right in the photo below). The tough one to get is the big silver smog sticker that goes on the upper left flat of the front cowl; you can see the location in the photo here:
https://www.raysmg.com/Web Images/Edited/MG2006/P1010004.jpg
That sticker is only available from the guy in Florida that sells exclusively through Ebay. He's hard to get in touch with and doesn't do Paypal or cards...check only when I bought mine.
If I can take any more photos for you or help otherwise, feel free to PM me.
Ray