All you need to do is get the coil connectors for the 993 and put them on your 964 leads. Connectors are p/n 928 602 557 00 (or beru 0 300 513 124 / 1 kOhm) I did this mod in August and it required no modification to the car, a simple hole drilled into the 993 coil bracket, a piece of 6mm threaded stock which goes into the original lower coil mount, the 996 pack slips onto that and then the ignitors, a nut holds it all in. I got a little fancy and used a spacer to offset the coils from the sheet metal and a bushing to keep stress off the ignitors when tightened down.
Cost? about $125 for coil pack, $25 for coil covers and connectors, a few bucks for 6mm threaded stock and misc hardware. Less than an hour and my car has not run this good in ages. Had nothing but failures and a hefty tow bill with the Silver coils, car ran better with the 24 year old coils than it did with any of the Silver coils I tried and this is one of the best mods I have done performance wise
Pics of install, I used 6mm threaded stock with spacer and nut to hold the ignitor pack in original vertical position, no modification to car required. A hole drilled in 993 coil bracket is all it needed (for threaded stock to go through) \
