Guys, thank you so much for all the praise, it was worth the effort. I will post again when it is painted and decaled.
I cannot claim that the idea was mine, I think it was a post of Colm Flanagans where I saw the basics mentioned and a picture in Irish broad gauge carriages by Desmond Coakham on page 26 that gave me the idea.
JHB, the middle axle slides laterally and I have tried it over Peco med, large and three way points of code 75. Which worked ok