That is interesting indeed. I think I saw the Chuck/Lamar lineup do Pony Boy twice and they played it as an instrumental. No words. 

That sure sounds like Dickey on resonator slide guitar. Probably Duane's and Gregg gave it to Dickey when Duane died. Dickey is holding it on his 1974 solo album Highway Call.  Must have been an acoustic set at the Beacon. I saw a decent number of Beacon shows but never heard that one. 

The guitar is a 1930's Regal wood body Duane bought in Nashville in the late 60's. Duane played it on Little Martha and a few other recordings including on the Layla album. Dickey got it from Gregg when Duane died and used it on Pony Boy and is pictured with it on Highway Call. 

The guitar store in Nashville wanted $350.00 and Duane paid them $50.00 every other week until he paid it off. 

I read about the guitar some years ago. I'm sure Dickey still owns it. No way he would let that go. 

@robertdee Dickey played resonator on the original, but on this performance he's playing acoustic guitar.

They did an instrumental version during the Rogues tour, and Dickey and Warren played the full "Pony Boy" a handful of times too.

@porkchopbob Thanks!! I think Pony Boy is a fine song with a catchy melody and beat. I was fooled. It didn't strike me as an acoustic guitar on that Beacon performance from 1998. 

Dickey seems to have played it sparingly over the years post 1973. 

On Brothers and Sisters Dickey plays the Regal resonator and sings. Chuck Leavell plays piano. Butch Trucks is on percussion, Lamar Williams is playing an acoustic bass. Tommy Talton plays acoustic guitar.  Gregg and Jaimoe do not appear on the track. That is according to a Johnny Sandlin interview and the credit sleeve in the album lists the same. But at the end Dickey and Butch slap a hambone part on their knees with Butch chuckling on the fade. Butch said he chuckled when Dickey suddenly switched it up on him. 

One of my favorites, almost 50 years old, local radio station plays this tune…