A couple of pointers to look for Paul,

¹. the date of manufacture will be in 'MM YY' format but really tiny just above the stockline, (on the action) above the trigger.
². T 01 trigger has two adjusting bolts ahead of the blade, T 05 has one.

They were designed as 'magnum springers' so should take well to FAC springs etc, I think they max out around 21-22FPE in .22.