My 66 Nyer is the opposite (with a '72 disc brake setup). I actually reversed the lines by mistake a couple years ago when doing a brake system rebuild. Could barely stop the car. Don't worry about the different size line ends, you can buy adapters at autozone.
This is the tool to use. You can find it for a bit less if you shop around. But with recent inflation I am probably wrong. A very large C-clamp is the best way to mount the plate on top of the master cylinder. The chains are worthless.
if you break down the build plate on the inner fender here is a code for the radiator support size. The 26" was for A/C equipped cars. I suspect the radiator was preattached to it. that would make it a lot easier to assemble the car on the assembly line. Unlikely there would be an assembly...
Iwould try backing off the rear brake adjustment about 1 turn and see what happens. Also did you accidentally swap the front/rear lines at the master cylinder? Just a guess.
If the valve guides are worn it's likely the engine will backfire through the carb. If you have none of that I would discount worn guides. My engine used to backfire through the carb until I did a rebuild. Had the heads rebuilt with new guides and it never does it now. It wouldn't hurt to go to...
Conductivity isn't the issue. It's corrosion. The contacts sliding together makes the electrical connection. The dielectric grease keeps the salt, water and other crud away from the contact surface. These connectors are not environmentally sealed like modern vehicle connectors are.
Loose bleeder valves are a common issue. I went to a power bleeder at the master cylinder because of it. I would also run your finger around ALL fittings and look for any seepage of brake fluid. They should remain totally dry after they are wiped clean.
That connector needs a rewire. If the housing isn't damaged, clean it up after removing the terminals and reuse it, otherwise I have seen them on ebay. The terminals can be removed with long nose pliers, gently squeeze the wide end while pulling on the wire from the back side. Write down what...
Only if the low and high bulbs are on the same fuse. I thought of that when I converted mine to relays. Separate fuses in case one blows you have a backup. And always keep spares in the glove box. It also helps to use the plastic tubing to shield the wires from chafing. Low cost insurance...
Any battery mounted inside the vehicle needs to be vented to the exterior. The fumes from a charging battery can be toxic. Gen 3 Challengers use a battery mounted in the trunk. They have a vent tube exiting through the floor for this reason.