AMT / Ertl makes a lowboy trailer, I think they call it a drop deck, it comes with a bunch of powerline equipment as a load.
AMT / Ertl also made a Caterpiller D8H dozer which will fit on the lowboy. I don't think the dozer is currently in production but it is still fairly easy to get.
You can use the tractor of your choice to pull it.
I did a similar set up last year (almost done now, just a few little things I need to take care of), using a Paystar for the tractor. The dozer does not have a ROPS (the cage over the driver) but it is not a hard scratch building project to add one if you like. The D8H was built from the late 50's into the 70's, roll over protection was not required until 1972, many older dozers had a cage fabricated by the operator so there really isn't a right or wrong way to build the cab. The other two vehicles are a brush engine (60 Chevy) and a dozer tender (72 Chevy fuel and repair truck).
