The liner notes of the 2015 CD release 'The Boston Rag' (Go Faster Records GFR052) mention that the WPLO interview took place on October 17, 1970.
Duane Allman talks about Eric Clapton and the 'Layla' sessions and the Derek & The Dominos track 'Layla' was played during the broadcast.
But the album 'Layla And Other Assorted Love Songs' was not released before November 9, 1970 and therefore the WPLO-FM broadcast has probably taken place in November or December 1970.