Has anybody managed to remove the engine with the gearbox in-situ?
Or is there not enough clearance between the engine and right hand bulkhead to remove the flywheel from the bell housing?

I haven't... but...

https://www.fiatforum.com/members-motors/353941-monica-88-4x4-sisley-3.html?p=3530973

It's do-able but probably not much faster than taking it all out together and then working on them out of the car.

I find it less frustrating and easier to do a better job with them coming out as a unit - but it's just my opinion and preference. Enjoy the fun whichever way you decide.

Yes. I lifted the knackered engine out of Project Peterborough and dropped a 1242 in there without a hoist.

Get the front of the car on ramps. Free the engine from the gearbox, twist a bit and drop slowly to the floor. You can lean the engine over enough to get out from under the car. Refitting was more problematic as I had to bench the engine up, jiggle it and ask for some help starting the two top bolts.

Thanks for the help, it's out!

The Fiat main dealer way of doing it according to their manuals from memory is dropping it out underneath, in which case the answer is yes