I pretty much owned much of the stuff from this era. After sitting in boxes from purchase til recently I have been testing many of the engines.
Diesels with lubrication prior to running not hardly any problems running or pulling. I don’t pull a lot though. As me and my Dad were collectors (Dad more than me) these were never run So >30 years So that alone is impressive
Steam and tenders success rate has been less
From a pulling perspective, the biggest challenge is with the F3s
I have ABBAs for many of what was produced (e.g. IC, UP, SP, etc.). With the ABBA and passenger cars and I always bought the add on cars, only having the one powered unit, it struggles especially with any grade to pull that entire train. So had to drop the extra b and or passenger cars to run them