As Erik says, the F&S clutch kit is fine. It is essential that you use the release bearing that comes with the kit. Yes it has some plastic in the construction and does look a bit flimsy in comparison with the all steel ones. If you have fitted a steel one it is likely 6.5mm different in height and that is why you are having problems. Been there, paid the garage twice!. All the discs are the same B18/B20, even B20 in the 240.Look at the details here. It's the pressure cover that is different. Except in desperation, always fit a complete kit, as the diaphragm spring will have weakened over the miles.

https://www.classicvolvoparts.co.uk/parts.asp?carID=2&cID=31&scID=152&page=A_B18_and_B20_Clutch_and_Bearings