Having both a 65 and 66 Fastback (both San Jose, 5-11-65 and 10-18-65 builds), the screws are as indicated in the spreadsheet for 64-66 Mustangs in the Forum's library, 4 each required, 53016-S13 8-15X1/2 Oval Head 17/64, Phillips for 65 and 53008-S13 8-18X1/2 Oval Head 17/64, Phillips for the 66. Both types of screw are chrome plated and use a finishing washer 34968-S No 6, stainless (it's a tight fit).
Jim