I never did actually listen to Herschel Sizemore play it, but rather got my "break" to the tune from simply listening to my good friend Rick Moon play it in the key of A Major on his mandolin.
After Mary and I moved to Tennessee, I had nearly forgotten the tune when it would be played at local jam sessions. One thing I noticed was that everyone down here in the South played it in the key of B, so I'd just capo up a couple more frets and pick along with no problem. But then came the challenge: it was time to learn it on the fiddle, since every one else was already playing the banjo and I'd been relegated to playing the fiddle full-time.
B is not the world's easiest key to play in and "Rebecca" jumps time intentionally, so I sure had my work cut out for me. But after many attempts at playing it up to full speed, I'm happy to say "I've finally got it!"
The chord pattern is:
4/4 time: B x 3 E x 1 / B x 4 / F# x 4 / 3/4 time: E x 3 / 4/4 time: B x 4 / repeat from beginning
F# x 4 / 3/4 time: E x 3 / 4/4 Time: B x 4 / F# x 4 / 3/4 time: E x 3 / 4/4 time: F# x 4 / repeat the 2nd half of top line.