I had a KHS MTB from the 90's which has slowly morphed over the last 3 years into a utility hauler bike:
But the frame on it was too small for me, so I picked up a 2006 Marin Pine Mountain steel frame for very cheap, and built it up using most of the parts from the KHS (which itself was a custom build back in the 90s' by the guy I bought it from).
I had to come up with a custom solution for hooking up my kid/cargo trailer, due to differences in the frame dropouts:
It's first voyage to the grocery store since I finished building it up: