circuit info required

I hv this VHF preamp. I want to modify so that it can be used for FM 88-108Mhz. I want to change the input output filter. But i want to study the circuit first. Hence i hv downloaded & atttached .s2p files of the devices used. But they just start from 100Mhz.
I want to know how the designer has designed circuit & calculated input output impedance? On this basis how he designed VHF filters for preamp 48-230Mhz with 28db gain?
I hv just not calculated/tested the ferrite choke value.
I hv collected even the datasheets of the devices used. If required i can post it here.
I am newbie to RF, hence expecting experts here to put some light on the circuit used.