Agreed, whether it came from a motorhome or a pickup or a car, it's basically the exact same engine with mostly just some different accessories/brackets. And I agree, it will have probably have less mileage on it than something that was driven extensively.
Though I still don't like the idea of buying an engine that I can't hear/see running, it does not guarantee it is bad. Heck, you might even be able to use that as a bargaining chip in your favor. It does appear to be just sitting outside under a tarp with the distributor taken out, so hopefully it hasn't been sitting long getting moisture inside. Also that listing SUCKS, dude provided literally zero info about it and even spelled "big" block wrong, you could be dealing with an moron here. Proceed with caution.
I would say though, going from a 292 to a 454 would basically make it an entirely different truck, what a huge step up lol. That would be super cool if it is a good runner, but don't get your hopes up and throw money at it until you know more