Obviously, it depends on area. I don't know what rules are in effect for Chicago, nor how exhaustive their tests are.
I do know that the kind of stuff TOC is talking about is not likely to work in CA these days. It used to work, before they ran the cars on a chassis dyno, but not now. I know several people who have tried, every single one of them has gotten caught. The smog shops don't even bother doing the visual inspection or EGR test any more, because the tail pipe always flunks.
And here, a 76 would be subject to biannual smog inspection.
And it is still against Federal law even without the required inspection. As I said, not likely to get caught, but the penalties can be severe if you do.