Sleeving 340 for a Stroker kit

One of my mom and dad's best friend's who were life time friend's frim way back in high school. Mr. Larry ran a 409 with the 6 2bbl Offy intake in a Tri Five Chevy. Still had lots of stuff so saw plenty of it. He also had old films 8mm? Of track runs at the Old Laplace, Louisiana Drag way.
Years back in 1971 I had a 61 impala conv. with a 348 Had the same valve covers. A friend had a 409 . Never saw one with the head off. Weird design