Thanks for the info Graham
From some research ( all comments relative to the 1.6):
Bell housing custom to this application
Gearbox housing custom to this application
Gear set 1-4 from a Citroen CX (Type TBC)
Other parts ?
As chance would have it my brother has a selection of CX's and a spare gearbox, anyone any idea if the parts relative to reverse and its selection are from the CX box?
There are a possible seven gearboxes for the Murena, 4 for the 1.6 (506, 511, 2GE14 & 2GE16) and 3 for the 2.2 model (510, 2GE15 & 2GE 17). These will have differences which is why they have different version numbers, and without doubt various part differences. Some of this will be down to the different engine torques. Larger torque usually requires larger bearings, so one likely difference will be smaller bearings on the Lancia/Murena gearbox whilst the Citroen CX/Murena 2.2 would have larger ones. Others will be differences in gear sets and differential ratios. The upshot is that without knowing exactly what you have, with two outwardly similar boxes, you cannot say whether parts will be interchangeable.
As for fitting a complete other gearbox, providing it is from another Murena 1.6 it should fit, but unless you know how it drove before there could be problems as 1.6 gearboxes were especially known to have synchronising issues owing to them having been built with mismatched parts.
You definitely cannot fit a box from a 2.2 Murena as the casings are different.
I do have a 1.6 Murena transaxle but I'm afraid it needs overhauling and I haven't done that yet so it would be sometime in January before I could tackle it, sorry. And it was removed for that exact problem with a lack of synchronising so I know it will need new synchros minimum. Now owing the scarcity and cost of new synchro rings they would be around £250 for a set anyway and then there are all the other things and labour so no box is ever going to be inexpensive.
As to whether a part from one of those other boxes will fit, it will depend on exactly what has gone wrong and broken, assuming something has broken. But to find out what has gone wrong means at least removing the casing to see the internals, and if it is that part that was broken in my photo I showed in the other posting, that involves a major strip to get at it and replace it, but at least that part only has one number in the Murena parts fiche (for all boxes) so at least the part from another box should be the same.
Roy