From memory - my provisional license for bikes entitled me to ride anything upto 125 cc as long as I displayed L plates (I have held my full car license since 1983)
If I wanted to progress above 125cc with L plates I had to do
1. CBT
2. Motorbike theory test
3. Module 1 & 2

I think that having a pre 1997 license gives you the above entitlements
If in any doubt check the DVLA website - it has all the info you will need.