Ha, ha. It's not hard to figure out where Mayberry is if
you know anything about (a) Andy Griffith or (b) North
Carolina and parts of Virginia. OTOH, Shelbyville and
Springfield, KY are real towns that are not far apart, and there
were enough clues over the years on "Guiding Light" (and on
"As The World Turns," which specifically identified Oakdale as
being in Illinois and 90 miles from Springfield) to suggest it might
be Springfield, IL (my second guess would be Springfield, MO, since
Josh and Reva made frequent trips to Oklahoma, which is close to Springfield, MO).