Do I need a stall converter?

Depends on the displacement of your motor, what kind of performance you want, A/C or not, etc. If the cam is in a 340 (based on your sig), running a dual plane intake and vacuum secondary carb, no A/C, then probably not. However, single plane intake, double pumper carb, etc. then maybe. Either way, you'd have much better acceleration using a 2500 stall converter. I'm finishing up a 318 with the same size cam and have a 2500 stall in mine.