From a practical standpoint, I’d guess the parts availability for the El Camino may be slightly better. But there were several generations. I’m not sure which one you’re interested in?
There is a company called year one that only deals in parts for classics. But I’m not sure if you’re into originality. I believe that company sells aftermarket parts, but they should work just fine.
There’s no easy answer. Depends on your local ordinances. Every county could theoretically be different. And it’s safe to say the ordinances aren’t equally enforced
You’d be wise to hire an expert to thoroughly check out any prospective vehicles. Likely any car you’re seriously interested in will have been restored. You’ll want to see all the paperwork and talk to the shop(s) that worked on the car. You’ll also want to see as many videos and photographs . . . of the restoration . . . as possible. Both before and after pictures.
Do you want a fairly original vehicle?
Or one slammed on dubs with a loud exhaust, booming system, wilwood brakes all around, etc.?
hemmings is a publisher. they actually have several magazines, and I believe one of them lists cars for sale. The others offer owner profiles and stories of restorations, among other things