I think you need to do a few things before getting too far along here.
Its great your doing this project and want to push ahead, but a little prep will go a long way to getting to the end results quicker and safer.
You'll need tachometer and notebook to go with the timing light.
Use timing tape or mark the damper to extend the timing range that can be measured.
Write down both the timing and the rpm at several different rpms.
That way when you change the timing you'll have reference points. I like to plot them on a graph but thats a personal preference.
Chrysler's instructions hold true regardless of whether its a stock engine or a modified one. Clipped and posted
here
The changing RPM may be that its running a bit lean for the conditions.
Or maybe it has a miss because of wiring. This caught my eye!
??
View attachment 1716112377
That doesn't look good.
A few other things that would be worth straightening out.
1. Throttle return spring
View attachment 1716112385
2. Fuel line to carb.
It should be a metal line from the fuel pump to the filter that runs next to the water pump - not over the exhaust manifold.
A lot safer and a bit cooler. Keep the outlet of the filter higher than the filter inlet, but lower than the lin from it to the carb. That lets vapor vent through the carb's bowl inlet.
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3. Secure the electrical wires.
View attachment 1716112386
Not sure about 1970, but in '67 there was a hole on the battery tray lip to tie the negative to engine away from the fan.
Every year had small difference but the important thing is that wires are not flopping, and have some slack (strain relief).
While mentioning safety, make sure the battery is charged.
If you observe the ammeter pegged thats going to be real bad pretty quick.
If its stays at half way toward charge (20 amps) or more for a long time (10 - 15 minutes) that's also going to cause melting at connections.
If the ammeter is showing discharge when the engine is running, then the battery is supplying power to run the car and therefore the alternator is not.
