This is an overhaul/transport stand for a Martin Baker H7 ejection seat, as fitted to the F-4 Phantom. It should also fit other examples of the MB Mk. 4, 5, 6 & 7 seats as well. The rear fittings fit onto the bottom of the main beams, and the De-Sta-Co clamp in front tightens a bracket over the front of the seat pan. Typical aerospace workmanship and overbuilt quality, even if it is not a flight part. This was used in-house in St. Louis for build-up, overhaul, and transport of Phantom ejection seats. The tag on the stand just reads "McDonnell", so this dates the stand from sometime between 1959 (first flight of the F-4) and 1967 (date of the merger with Douglas).
A basic stand without wheels for the F-4 seat costs around $250. For a bit more you can get an actual McDonnell stand, with wheels for wheeling your seat around into the family room to watch football (or whatever you prefer to watch).
The last two pics are of the actual aircraft this cart was used with, s/n 63-7763, a USAF RF-4C that was used in Vietnam, before returning stateside and used as a ground maintenance trainer.
If the listing is up, it's still available -- no need to check on status.
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