This is just a thought ,, if you can get an engraver and letter and number punches , do all your engraving and punching to what your happy with, paint your main colour (spray with acrylic auto paint) a few coats , let it dry then paint all the engravings etc , then when that drys you can block sand (wet and dry 600 )over the top and it will take any over paints out and leave the colours in the low spots , when that drys give it a few coats of clear,
Only a thought