In the late 60s or early 70s some car companies tested their old engines for emissions. They were surprised to find the old long stroke flatheads had very low emissions.
The long stroke design is particularly good for NOX which was quite a problem for a time. Car makers redesigned their engines with a longer stroke about this time. Engines like the Chev 305 and 307, Chrysler 360, and Olds 400 were small bore long stroke designs compared to the typical V8.
So if your old engine is in good shape, not burning oil, and tuned up well with a good carb you may pass the emissions test with no mods. If it was me I'd try it anyway to establish a baseline if nothing else.
