[Amps] Motorola app note eb-63 question

[Dan Sawyer]

I am trying to convert an ENI TH430 based RF power amp to 'mimic' the EB 
63 circuit. Can someone provide a starting point for the purpose and 
selection of C8 and C9 between collector and emitter? What is their 
purpose? How is the value calculated? What are the circuit parameters 
that influence the value? What are the transistor parameters that 
influence the value? Thanks - Dan