I think it is located between the starter and the bell housing.
The Murena 2.2 does not have any plate between the engine and gearbox.
The Murena 1.6 generally does not have a plate either but some of the Simcas were fitted with this plate and if you have one it is a good idea to fit it. Also there may be a support plate at the end of the starter motor furthest away from the bell housing. This is definitely worth fitting.
The problem is that the starter motor on the 1.6 is bolted to the bell housing and this part of the bell housing can break off complete with starter motor and fall down, possibly shorting the electrics too! It has just happened to one club member. The support plate will prevent this happening.
The starter motor on the 2.2 is bolted to the cast iron engine block NOT the bell housing. Since this is stronger, you do not have the problem which can afflict the 1.6 model.
Roy