Depends how much boost you want to run. You can get away with 0.4-0.45bar on the stock C/R with intercooling and the appropriate changes to fuel & ignition timing. Any more boost and you have to decompress the motor.
You wouldn't have to upgrade the rods... they are the same as the Carrera/930 turbo rods. Just upgrade the fasteners.
Common practise for the 964 motor is to machine down the crown of the pistons, since they have a lot of "meat" on them. You can get them down enough to run ~8.5:1 C/R and run 1.0+ bar
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition