actually no. Danelectro already had roundwound strings on this basses (probably heavy gauge guitar strings, considering the small tuners and bridge), and John Entwistle used to buy a new Danelectro when strings went dead, because there were no roundwound strings on the market.
he had Rotosound produce them, but at the time the Fender basses were not the "standard" anymore; the 60's were the era of short scale basses (hence the "long scale" used to point the Fender basses, and not the standard scale).
while listening, I thought about a P with rounds, not flats. however we'll probably never know!
coming back in topic, bassist from Greta Van Fleet uses a P with "very old" D'Addario flats:
You’re probably right about Head East..... I just always post that in “best....whatever” threads because I like it so much....relevant or not. Lol.