I recently did this for my Rapido FL9 by using spare Kato F unit numberboards, they also sell the numberboard blanks for SD70MAC, AC4400CW, that you could probably repurpose for your other locomotives.
The numberboards come on a sprue runner made of the same translucent plastic material that could be cut down for custom sizes that aren't available, (like the SD80MAC rear small numberboards)
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