Aristocrats replacing key framework (6)

I believe the answer is:

gantry

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'framework' is the definition.
(I know that gantry is a type of framework)

I can't explain the remainder of the clue.

(Other definitions for gantry that I've seen before include "Support for a travelling crane" , "Overhead structure for such as crane" , "platform" , "Bridging framework to support crane, signals etc" , "Metal framework for crane, signals, etc" .)

I've seen this clue in The Times.

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