You have to be a tech or go thru a dealer to get your hands on the boards. There's no kits available that I know of for HO scale. So you'd also have to order the harness I would think? Unless you had a donor engine to scavenge the stuff out of.
My go to guys were GGG here on the forum and Ray's Electric train works among others.
I can't get the boards direct myself as I'm not a tech. If I could, I would try to install into my Lionel trackmobile! I do my own personal installs in G scale and O scale 2 rail.
You could try some tech/repair person to attempt this. I think one that has experience with the MTH HO line repairs would/might consider trying. They should have the chart for the pin outs where I'd just be guessing!
Sorry to take so long I thought this was posted in the DCC forum and I didn't see it there. I did get your email earlier.