[rovertone]

A friend of mine had a vw golf as his holiday home runabout in Portugal and the headlining sagged to the point that when I drove the car, being tall, it rested on my head.
As a quick fix for him I used small pearl headed notice board type pins inserted through the cloth at c 45deg angle, I spaced them in rows approx 6" apart same between rows and it was very effective, so much so that several years later its still unchanged. Had I realised this I would have put more thought into using other colours and been a bit more uniform with the pinning pattern.
I am not advocating this for your 75 but it would work for holding back any sagging if its causing a problem while you sort a permanent fix.
Incidently this is a common problem on Golfs especially in hot countries and if you search on You Tube for headling replacement there are a number of videos showing what is involved to replace the lining which I guess would be similar to our cars. A messy job!