Did Dassault have some magic trick up their britches
It was an era of innovations. Have you seen the Vickers VC10 thrust reversers? The clamshell / target doors can be made internal within the nacelle. Literature is lacking on the Mercure, but there is a nice hint from a cutaway drawing:
Source: Air Enthusiast magazine, via aviadejavu.ru
The highlighted ...
You're asking about turbine (hot) reversers of early high-bypass turbofans.
flickr.com and twitter.com
It had the same mechanism as the cold bypass (blocking doors), similar to what the C-17 (right image) uses nowadays.
Lockheed L-1011 TriStar - Airliner Tech Vol. 8
It had target-type, but only during development.
Design Features of the ...