My all red export lenses have amber led,s in the indicator part of the lamp unit.... and they shine amber through the red lens, so no probs with people not seeing them as they might if they flashed red.
I'm looking at a RFI buffer unit, listed by Spiyda Design... they say that their little box of tricks converts RVI tacho,s to RVC tacho,s with no dismantling of original tach... just an add on. I have emailed them on more info etc. If it is all correct its about 1/2 price (£40) of getting your own tacho modified.