Is the base plate for a specific tow bar/brand? I just ran a search on Roadmaster's web site and they show brackets (their name for a baseplate) for that truck, although there's a note saying that, due to slight variations, you'd have to make a measurement or two to ensure you got the right one. Click
here for their search page and scroll down.
One more caveat - it says "no diesel" for that truck, so presumably that means gas only, although I have no idea why.