I, like you, have bought some 20 yrs ago overland diesels and have never put them on a layout or even a test track. I was more interested at the time, as I was into HO, to have mantle pieces to just look at. Just the bulk of O was so enjoyable and buying a piece a year was managable at the time.
We moved and the new house wasn't big either but had land so I got an old office trailer, 11x 40 and started a HO layout in it. I had so much trouble with the rails expanding and contracting I gave up as I wasn't living in it to wish to keep the temp. even at say 75'. That was about the time I decided to try O scale as the rail wasn't as tempermental as HO and I could leave a little space between the rail joints for the expansion. The O scale wheels would be able to ride over the gaps easier than the HO.
So, I ripped up the HO track and in its place putting O scale track using the same framing. The hardest part in all this is to get a grasp on the dimensions of scale, just how much one can use the space and with O, it ain't much. 40 ft. with a turn around at each end leaves less than 30ft. or about a train of 20 cars on one side of the room. One can get dizzy going around an around following his trains as I liked mainline running.
BUt back to the Overland, I'd be a buyer of 1 or 2 more in the future at the right price especially some newer 3rd gen GE units.
But since you mentioned the overland question I need to unpack them from their green boxes and take a look at my 2 U50s and one SD 40-2. A nice something to do this weekend.
Phil