Bill. You must know someone who can take a pic of this beast? Then all of us can chirp in with your answers.
I never heard of a factory diesel loader backhoe set-up on a 550, so it could be an aftermarket set-up. There were a few available.
It could be a 1550 or 1650 too. I think diesels were used for those models.
Send a pic!

Here's my 550 loader/backhoe (being late 60's it is called a White 2-44 13LL as White had purchased Oliver by then)