Reach out to Jim @ PPI, he has the correct 82-93 SSP oil cooler O-ring gasket as well as the correct gaskets for the 84-86 SVO’s and the 94-95 SVT Cobras.
I have purchased a few from him…
He has quite a bit of rare/hard to find Fox Mustang SSP parts as well as SVT/SVO parts. Great guy and I’ve been dealing with him for over 30 years now.
https://www.performancepartsinc.com/
https://www.facebook.com/PerformancePartsInc/