Your take on a potential trade.

74 Dart sport came with a 360 if its the stock block.
My 74 Dart Sport came with a 318, A904 and 8ΒΌ Open Diff.
I wouldn't even be considering a swap until you know what he's got and it's condition. You know yours. Is he willing to provide all the info and receipts? What is it? How old? Who built it? What pother parts in the driveline were upgraded for it? Are those included too? If he doesn't know, that's not his fault, but it's certainly a big risk to you. Even in terms of just having an engine in the car to drive around.
I haven't even talked to the owner. It's the shop's owner that asked me if I would be "interested" in trading engines. The opportunity is neat for a performance boost but "keeping it # matching" kinda ranks higher in my opinion. Just for the sake of it still running great after 44 years.