Those would actually be very simple to mask. Paint the yellow first then add strips of masking tape cut to the right width and laid out like the 7. The apply the camo and peel off the tape. Presto.
That seems easy enough. It's the simple things you never figure out. Thanks CR for that. I will give that a go when I finish up my 2 1/48 B-25's,1/32 HB Spitty vb, 1/32 Rev P38 1/32 Hase F6F and my 1/32 Rev P47D. Should have them all done within the next few minutes
Always it is possible to either print a such digit on a clear decal sheet or make them as Terry suggested above. Of course there are other ways for making them but these need some of patience and accuracy.