I swapped out a 65 273 for a 69 340 in my 64 Dart, I had power steering, no AC and a 833 gearbox. I could not get any iron manifolds to work mostly because of the steering and had to go with dougs headers and a uv joint from flaming river to get the steering to work.
Talk to
@waggin, He did most of the work.
You will need to upgrade your radiator as the 273 rad will not be enough.
Also the hood clearance is really tight.
As for the torque converter that is more related to your CAM and gear ratios. You will need at least an 8 3/4.