In his 911/912 authenticity book, Brett Johnson wrote concerning the 4-screw dash, "The newest car in my file which had these is 301175." He doesn't claim to have complete data, just none beyond 301175. I can add that 1965 Porsche 911 chassis number 301258 has it's original dash and it is the 4-screw variety. I am just guessing now but the 4-screw dash may have run through the end of the 1965 model year production somewhere around chassis number 302010.