Exhaust smell in cabin

[chewiebarker]

This is a somewhat broad question, but I searched prior posts and I really don't know where to begin to fix this.

My kids keep complaining, and I agree with them, that the cabin stinks of exhaust fumes (and gas fumes to some extent) when we drive in my 1971 K20 Suburban. I suppose there are lots of possible causes but here are the things I wonder about perhaps being the cause.
1. The seals on the doors are all screwed up, or missing
2. The PO vented the exhaust out the side of the vehicle in front of the rear wheels. The exhaust runs straight from the headers into cherry bombs (brand unknown) and out. No muffler of any type.
3. Old cars just stink.

I am less suspicious about the location of the pipes because I have seen other people exhaust their cars at that location without complaint of fumes and I assume that while moving the exhaust would trail behind regardless. It doesn't seem to matter if the car is actually moving or parked. No matter how fast I drive, it still stinks. Is it typical and to be expected that these old trucks are just going to stink? I don't know where to start to try and remedy this (other than take it to a shop...$$)

Any advice would be appreciated!