There are plenty of things to rattle inside and under any car. If it is a clunk, it is more then likely underneath like exhaust or as someone mentioned a shock. My charger had a rattle I thought was in the deck lid. I finally found it a while back. It was the torsion bars for the deck lid...
I'm not an engineer by trade but I do consider myself a "field engineer" meaning I have engineered some fixes for things that didn't work.
However, I have to admit I have messed up a few things that were engineered properly that I made to not work properly.
A couple things come to mind I know I...
I have to disagree with the last part of your comment. If the oil is black, it is dirty not burnt. I've always been told "Oil never breaks down. It get dirty and contaminated."
If the cruise kicks in but slowly loses speed, the diaphragm is losing vacuum somewhere. If it won't start at all, it could be any number of reasons. Even a brake light out or a bad connection.
This is a Used bumper jack removed from a 74 Challenger that I parted out years ago. It is the base and jack assembly for the bumpers with jacking slots. No lug wrench. Has some surface rust and would be a good candidate for restore.
Driver quality as is. $55.00
Free shipping from 54703 to USA...
I have not used the "Cold Hose" vendor but it looks like maybe they are the go-to people if you can send them your parts for rebuild. My car needed custom hoses and I used a local high end restoration company near me that has the crimping tools and hose for One-Off fabrication. Extremely spendy...
This bumper jack and base came from a 74 Challenger that I parted out. It is for the bumpers with the jacking slots. Probably fits some B body bumpers too but for sure 72-74 E body cars. It would be fine for a driver as is. Jack and base only. No lug wrench.
$20.00 plus shipping from 54703...
3/8" fuel line with 1/4" return. The design was mostly to alleviate vapor lock on 440 and Hemi engines along with the vapor separator shown in post #2
Note: I would not use the filter type shown in the last picture unless it has the metered orifice for the return. Most of those filter units do...