Sandcrawler - trying to find these parts

Dipping my toes in the studio scale pool and after reading, reading and more reading of hundreds of pages of threads I think I will begin doing some research and begin on a star destroyer. I couldn't help but notice many models from the same kits used on different models and one has got me scratching my head.. Its on the SD and the sandcrawler
Looks like two parts connected together and not one single part.
Any ideas?

Re: Trying to find these parts - they are on several models - dipping my toes in

The top part looks like from the mack truck but the bottom part doesn't.

Re: Trying to find these parts - they are on several models - dipping my toes in

Anyone?

Do you have any additional pics of the same part from a different angle?
Maybe a wider pic too that shows it's size in relation to other known parts.

L