I think you have two problems: poor adjustment and marriage of kick down linkage to carburetor; and carburetor type and tune issues.
First what carburetor are you using, and does it have vacuum secondaries?
Does the throttle plates fully open when accelerator is planted on floor boards?
When operating carburetor by hand, can you see the throttle lever on transmission fully swing its ark, and still allow full throttle plate opening (WOT)?
but first gear seems to shift very late at high rpm and my transmission does not down shift when I floor it.
This is caused by too much throttle pressure, and rod needs to be adjusted to allow less pressure at low rpm. It may be that the carburetor’s throttle shaft geometry won’t allow your current setup enough travel to play nice with the transmission. You may need a Chrysler throttle adapter for your carburetor...can’t tell until more details on carburetor are reviled.
Furthermore if I am at idle at a stop light and I hit the throttle pedal to the floor, my car lags as if it is going to stall and then it kicks into gear and accelerates after hesitating for a second
This is a carburetor tune problem. Generally a flat spot, or bog at off idle acceleration indicates a temporary lean condition during transmission from idle circuit to main jets, but can also indacate a too rich condion as well; I'm betting on lean. In other words perhaps a larger accelerator pump shot, or a longer duration shot will cure this. I’ll ask again, vacuum, or mechanical secondary’s? This is important because a light car with a small displacement engine is real hard to tune with a mechanical secondary because they can open too soon when there is not enough air moving through manifold to support proper air fuel mixture on a slant six. In other words it is a giant vacuum leak being introduced temporarily, or does the car blow black smoke on hard acceleration form a stop?
I need more information on your carburetor, and state of engine build to help much more.