Renbourn plays it in EADGBE, in E major, and I think it he did it the same in the Pentangle version, just tuned down a half-step.
A quick google for "Lord Franklin DADGAD" brought up these two:
https://ozbcoz.com/Songs/song.php?ID=3304,celticg (only chord shapes, no fingerstyle patterns)
http://www.jimronayne.co.uk/FranklinB.pdf (fingerstyle)