yep, just take your old one with you and try to match it up as closely as possible. The one I just bought for a 63 Impala was actually for an 85 Camaro, the ports were just a little different, but the mounting is the same.
To check if the pushrod is working, take the pump off, take the pump backing plate off, and hold your finger on the end of the rod while someone cranks the car, it should stroke about 1/2". When you go to reinstall it, put some lithium grease on the rod to hold it in the block, otherwise it's going to be a PITA to get the new pump on.