50/60Hz mod documentation needed


I have a newer model of the Sega Master System 1 which doesn't have the built-in snail game, etc. When I got a document detailing how to add a switch to play 50 or 60Hz, I found that the inwards of the Master System it was describing was different to the one I have, therefore I can't switch it. Does anyone know of any documents out there on how to mod a newer SMS1? Pictures would be nice too, but just the document would be great.