I realized this intro has been done so much, but I'm going to post it anyway. I was going through all of my videos to update them with a tab player for my site and noticing how horrible my version sounded to me, and I think I figured out why.
Basically I thought that the 2nd measure where he drops down from a Bb to Bb79 was using an open 6th string to get the Ab, which I believe he is using that voicing but not that way. I watched a Travis Toy video where he does a version of Rose Colored Glasses and saw how he was doing the b79 chord voicings and then figured out a better way, using Travis's way of voicing. Many of you probably knew this already, but it took me like 3 years. Who knows what I'll think of it another 3!
This is how I've been playing it for many years, except a half step lower to accommodate our singer. Many of the online tutorials I've seen show 2nd to 3rd measure as 6AB→6→1AB. Problem is that playing it a half step lower, would involve a slide down to open strings. So I worked it out the same as you show in your tab.
Ironically, I just revisited this intro because I wasn't happy with my performance, When I listen closely to the recording, I don't hear that smooth transition (slur?) with the 4A→4D in the 2nd measure. The 4D sounds more like a pedal down → pedal up on the 6th fret to my ear. Basically the same notes, different fret.
-----4--------------------
--4--4--------------------
--4-----------------------
--------4-----------------
--------4A-----6A~6 →3----
---------------6B~6 →3B---
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----------------6~6 →3----
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1980 MSA Vintage XL S-10, 1975 Session 400
1972 Dobro model 66s
Derby SD-10
Tom McDonough