The 25 I di has quite a chunky grill, the 20 proto has a fine grill with a circular frame Mmmmmm....
Then it came to me when I was cutting a piece of drain pipe today, the 50mm circular frame could be a slice of 50mm water pipe. As for the grill I started looking in my garage and found just what I needed, some plaster board jointing skrim :)
Glued on the top with a cross support made from a couple of styrene strips
Then a quick rub down and wash followed by what i hope is a final coat of primer.
Once its all dry I can now move on.. Yellow then I need to get some Railfreight grey