It's taken a couple of days to get time but....
First off, all the slave cylinders are much of a muchness, except for what I call the ears (flange LR call them).
Here's a quote from the parts book that should answer the OP's original question......
Clutch Release Mechanism - R380 Box with V8
"Slave Cylinder - UKC8677L NLA - Use FTC5071 which has thicker flange that elimitates the need for backing plate FRC2402" Hope that helps
Richard