I'm working on my overhand shuffle, but I didn't notice any detail regarding right hand index finger position (shuffling right hand into left) in any of my books/DVDs.

Thumb and ring/middle fingers grip short edges, pinky useless. But judging from video footage of performers sometimes the index finger curls behind the deck, sometimes it sits on top of the long edge, roughly in the middle (perhaps slightly curled over).

Have I got this right? Is the position of the index personal preference, or does it make a difference?

It'll pretty much be whatever floats your boat. My preference is to curl the index finger over the top longitudinal edge of the deck.

FWIW

Depends on your application. Generally right index finger goes along top edge. However, some applications, like the optical false overhand shuffle have it along the front edge.

You have read Erdnase yes?

I learned the O.H.Shuffle from Royal Road to Card Magic.
The finger adjustment on the book works really
Well for me.
Check it out!

Same here. Royal Road to Card Magic is quite detailed on finger position for both hands, which is a huge help for jogs.

Good calls - I missed the detail regarding the index finger in my books (that'll teach me not to double check). Both RRTCM and Erdnase say to rest the index on the top. But unless I missed something (again) they don't say why. Anybody know?

Edit: it seems that Aaron Fisher notes that the index finger is used to control the bevel of the stock - which makes good sense

*sigh* How much easier would all this be with someone who really knew their stuff teaching me in person. Oh well ...

Get Aaron Fisher's Pathway to Mastery videos (the first one is what you'd want but they're all excellent). He teaches all his students the overhand shuffle and his videos are very detailed. He's a fantastic teacher.