Rotella oil is ideal for older cars without catalytic converters and for which zinc was a requirement at the time for engine oil. It eliminates the need for adding a zinc additive to modern oils.
Yes a battery tender is a MUST. Not charger, maintainer. I have 6 maintainers on my cars.
here are two types I have
https://www.amazon.com/Foval-Automatic-Trickle-Motorcycle-Batteries/dp/B081ZR7JZ9?ref_=ast_sto_dp
https://www.ebay.com/itm/323903074556
Check the bulk head connector under the hood, Blue and gray wires, one wire is 12volts when cranking and the other is 12volts when on. Also check the connection of the red wire on the steering column. I had the same problem.
I have 2 sets of lower control arms one with sway bar tabs and one without also a 2nd K frame. I'll get pictures of the lcas if you need them. I'm not sure what to ask for these parts, also you might want to think about shipping cost, I'm in L.I. N.Y. 11756
I have this really nice k frame from a 74 Challenger. The only difference I know of the 74 has the extra motor mount "stabilizer" at the motor mount area, this limited the engine from torque twisting.
I know this sounds dumb, but clean off ALL the old grease with brake clean or carb cleaner, it will also remove PAINT, once it is clean and new grease is applied the window should roll up and down easily. I know I had the same problem.