Stepdad imports cars newer than that all the time, but they meet current standards. He (and his partners) have brought in 1000s of cars from Canada.
The cars he has tried to import that do not meet current emissions/crash/dot standards can be imported, but cannot legally be registered for on road use (off road only).
He went through this some years ago trying to import those little mini trucks. The first one they brought in could not be registered (ever) because it did not meet current emissions/crash/dot standards. He could get as many as he wanted in the country, but they could only be used for farm/off road use which severely limited who would buy them. The venture was deemed not profitable and they stopped trying. IIRC the law said the vehicle has to meet current standards of the day it's imported. NOT the day it's built, like the old law for domestic built vehicles which USED to be grandfathered in (and no longer are by state law).
So basically, you import a car built in 1958, TECHNICALLY it needs to meet 2020 standards unless the car was previously imported.
This is the same thing you run into building kit cars. TECHNICALLY the kit car has to meet the current standards. Used to be you could use a title for an older vehicle (say a Falcon) to title a kit built Cobra (for instance). STATE law expressly forbids this in Oregon, but enforcement is lax. State law says you may not alter the appearance of a car to make it look like another make or model of car. People still do it all the time, and it is absolutely iegal. I went to court over it in CITY court, and the judge said the law was ridiculous and threw the case out (liberal judge). However, just because a liberal judge ruled in my favor it doesn't mean the DMV has to issue a registration.
Note the difference between TITLE and REGISTRATION. You used to be able to get off road vehicles titled, but not registered. I have no idea what the policy is now, because I haven't screwed with this stuff in 20 years. I have probably 8 vehicles with titles right now that cannot be registered (unless you count an off road tag as being "registered".
As was pointed out, you can get the vehicle in the country, sell it with a bill of sale, and possibly get it registered, but it is not registered legally. Does anyone care? Probably not. One of my kit cars was done that way. In Oregon, if you went to the Salem DMV, you were fxcked. If you want to a small town in eastern Oregon, they didn't bat an eyelash.
Like I said, I've been out of the business for years and maybe things have changed. In the 90s it got really difficult. Anything before the mid 80s, they never even cared.