Th vehicle may be new to you but the A/C system is 50 years old. Unless you had it rebuilt in the last few years. The hoses can't be trusted and need to be replaced. You need to remove all the R-12 oil too.
I don't know what chrysler changed between 66 and 70 on A/C units but the basic system should be the same. What I did to rebuild mine was rather involved. I changed the compressor to a sanden unit and converted to R134.
You may want to but a new condenser, they typically get beat up and have bent fins after 50 years. I highly recommend going to a sanden compressor. They are low cost, and readily available. The old harley v-twin compressor costs over $500 for a new one if you are lucky enough to find one.
It went like this:
1. Buy hose crimping tool, new receiver/dryer, hose ends that match existing threaded connections, A/C hose that matches existing sizes.
2. buy A/C flush in pressurized can from NAPA, disassemble hoses except for outlet hose of evaporator.
3. remove expansion valve (be careful with the thin temp control pipes connected to it. You will need to keep the large pipe they connect to.
4. Place outlet hose end in empty milk jug. Use ac flush at evaporator connection and blast A/C flush through it. It will be rather nasty coming out. Flush out all solid lines too. And condenser.
5. Carefully cut off the crimped connections from the large pipe mentioned earlier.
7. Using original hoses as a template for new hoses, make new ones. Install them as you go. Install receiver/dryer, and condenser if you bought a new one.
8. The pipe the goes across the back and drivers side of the engine can be replaced with an aluminum pipe. You will need to use a propane torch and a thin piece of aluminum to braze the threaded ends on to it. My brother is an HVAC guy and has a tool that will bend it to the right shape. Keep the old one as a template and ask an hvac guy to bend the new pipe to the correct shape. It is not easy to clean out the mufflers in the original pipe. The crud in them will damage the new compressor. So I eliminated them. Here is a couple photos of what the finished system looks like.