Sure, you can use the 964 style bumpers with the pre-89 tail-lights. I've seen a few cars like that and it doesn't look too bad. The 964 bumpers, whether for narrow or wide body 911's, will mate up with the rear quarters nicely.
If you want the 993 look, you have to change all your quarter panels/fenders. Could get quite expensive, but it'd look very slick
'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