It's a surge tank, not an overflow tank. I believe Matt is right in that '64 was the last year for them. However, for whatever reason the FE engines always worked best with the surge tank. I'd go ahead and put one on your '65 if you can find one Tyler. Heck, I ran one on my '66 pickup with a 428 CJ engine for a couple years with no cooling problems. Maybe G or somebody can explain to both of us why the FE's work better with the surge tanks. I don't know why they work better, just that they do!!!!!