Should you decide to go ahead with the purchase, I would check to see if there is a ballast weight attached to the box that holds the backplate. Early U1 frames, such as mine, did not have this and the speaker is nose heavy and can be prone to tipping w/o the backplate installed.
The first picture I posted shows the result of this imbalance when a tube trap fell over striking the frame with the backplate removed causing it fall over and hit the wooden arm of a loveseat. The core was returned to SL for repair, which was done for a reasonable cost and timeframe. Actually, the total shipping cost was much greater than the repair cost.
Anyhow, I purchased 1/2′ steel plate and glued it to the rear wall of the box of both speakers to prevent a future recurrence. I would recommend doing the same if no ballast weight is present.
Good luck with the purchase,
John