Pan fill had the dipstick tube going into the oilpan. Case fill has it going into the case, just behind the bellhousing. Unless you'rs has been swapped out in the last 30 something years, it's a case fill. You may also need to count your bellhousing bolts to see which housing it is, early 65's ( also known as a 64.5) had a 5 bolt bell. The later 65's were 6 bolt.
Watch for bell housing design too. Some bolt to the case with the pump bolts. Others use a larger bolt pattern seperate from the pump bolts. I've heard pan fills are all 164 tooth flywheels, but can't say for sure.