just because dennis does it, that doesn't mean it's
physically possible.
If I can tongue block an overblow pretty much anyone can learn it. I
have a harder time tongue blocking the 10 blow bend. One thing that
really helps is having a harmonica that overblows easily. It took me a
while but it wasn't any harder to learn than learning to overblow
pucker. The only advantage I might have had is I tongue block 70/30 the
lower 7 holes, actually it might be 60/40 depends on what I'm playing.
Mixing threads here, I think the reason most right handed people hold
the harmonica in their left hands is that the cupping effects are
physically more demanding than the actual holding. The dexterous hand
ends up being the cupping hand. All of that other technique evolved
from there. You can hold right and get the upper end of the harmonica
sealed against your cheek it's just harder and a different technique. fjm