Which radiator?

Whatever you do, don't follow me and use the later aluminum water pump in my 1965 Dart w/ OE 273. It is 1" longer, which will cause many headaches with pulleys, radiator clearance, and even the power steering pump (TRW pump doesn't bolt up). I only did so because a newbie and its outlet side matched the only radiator I could buy from Autozone. I am long beyond Autozone these days. I eventually got everything to fit, but had to be extra creative. You can install the earlier cast-iron water pump. Otherwise, your 340 engine should be identical to the 273 V-8, if your car came with that. If originally a slant, you will need the cable throttle and a V-8 steering cross-link, plus a few engine wiring changes.