A friend had one of these back about '76 or so, in my college days. His had the removeable cloth top. It was basic transportation that got you there and back. It was noisy, underpowered, and slow. It was impossible to secure anything inside. Fred had his radio stolen from the thing in broad daylight there on campus. Even though the doors were locked, someone pulled the door or window away far enough to reach in, unlock the door, and pop the radio out.
It was also a blast to drive. We took it down some motorcycle trails out in the boonies, and got places that would have been tough to get to with most any other 2WD vehicle.
If this will be your daily driver, I’d forget about it. If it’s a toy car for bombing around in the summer, then it might be fun. If you really like your sister and your almost-a-BIL, then look around and see what other Things are going for. Hemmings lists 4 of them, for $3500 to $5750.