Can someone explain stroker kits

The best examples that I know of re: "factory" strokers are Chevy.

You start out with (I know, 265) but let's say 283

265, 283, 302 (we used to call 'em 301) are all same stroke.

I believe 307 were 327 stroke cranks in a 283 bore block

327 was a 4" bore block stroked, and 350 was stroked again.

So 302, 327, and 350 all used same 4" bore, just different stroke cranks

On later 350s of course the main bearings were larger. I don't remember all that anymore, I think some of the 327s were larger main sizes, too

267 and 305 was 350 stroke, smaller bore

400 was a siamesed block, just like the Chrysler 400 and was both bored and stroked over a 350

Now, this does not mean you can easily convert. There were changes over the years, in main bearing sizes, etc