Wouldn't be easier, and cheaper, to buy the MTH version? The Williams scale version is selling around $320. They do have a "semiscale" version which is much larger. That is going around $150. The MTH has PS3 with electro couplers. Also, it is a Premier product so it has a lot of detail. I found it listed as low as $399. An ERR upgrade, not including labor is going to be about $150.
I see pricing for both scale version vary by road name.