I have a Kenwood am/fm with Bluetooth capabilities in my 73 Challenger. In the rear I have two Alpine 6x9 speakers that came with the car. When the dash was out I put a two speaker replacement in for the original speaker. Frankly, the dash speaker sounds great and is loud enough to be heard over...
I used Topher Mcguiness this winter to rebuild my wiper motor. He did a great job and it took about a month to complete. I had no problem whatsoever and wouldn’t hesitate to use him again. He is on the internet as The Headlight motor Man. Nice guy and he can do much more than just motors.
As far as leaf springs go, you can get anything you want from John R Spring in Madison Heights, MI. They will build it and ship it to you direct. They have been around forever.
I put an Edelbrock AVS2 650 on my 73 Challenger 340 last fall. It worked great right out of the box. It runs smoothly and starts easily. Highly recommended.