On one of my builds, I used a cat 144 skid on a 151 track. According to Mountain Magic sleds in Edmonton, Alta, you can set the skid back up to 8" from the drivers to the tip of the skid without running the risk of spearing. Hope this helps you.
The way I understand it, is that all you have to do is move the mounts 4" back from where the mounts would be if you were making it a 136". There may be more to it, I don't know.