Happy to say that my home made masks turned out a great result. The masks were made on vinyl transparent peel-off sheets using a Cricut digital cutter with the insignia files cut and pasted from my pdf drawing and sized on the proprietary software for the cutter. Following is the sequence of application. I started with the underside so that I could try out the technique and colours first.
The full disc of the mask was first carefully placed on the model and the area surrounding the roundel was further covered with paper to prevent overspray.
The first challenge was in trying to get the mask to conform to the surface around the aileron actuator bulge. The vinyl is quite stiff and kept lifting up when I pressed down to make it conform so I ended up cutting slits in the mask. I then sprayed a layer of white.
Tamiya paints dry almost immediately so there's no need to wait before applying further masks over freshly painted surfaces. Once the white was done, I placed all of the mask rings within the painted disc, making sure to line everything up perfectly so that there were no gaps or overlaps:
The mask portion covering the blue ring was then removed and the blue applied. For this I used Tamiya XF-8 Flat Blue with a tiny drop of XF-2 Flat Black
Seeing that I could control the spray fairly tightly, I didn't bother putting the blue mask back on and went straight to the center red dot. After removing the mask, I sprayed Tamiya XF-7 Flat Red with a touch of black. All paints were thinned to a ratio of about 40 paint to 60 thinner.
To my surprise, the reveal showed absolutely no sign of bleeding so no touch ups were needed.
Here's the underside with both roundels done. My only issue is that I think that I added too much black the red and blue so the colours don't quite represent the "bright" insignia colours. I'll adjust this for the upper surfaces.
Thanks for looking in everyone.