It could be that your ST prefix was assigned as a ways of Identifying your Winchester model 63 as one of the recently made models.They were reintroduced for 2 years in 1997-1998.The original model 63 rifles were made from 1933-1958.
Receiver
On the receiver
Receiver/barrel
Look at the receiver
Receiver
Check the receiver and barrel
Receiver.
Receiver.
Check the receiver.
barrel, tang, receiver
Bottom of receiver
Check the receiver and barrel.