F,b5 interval?

I'm learning Chuck Berry's "Johnny B. Goode" in key of Bb

re-writing the tab out by hand

then along the top I'm identifying what key each of the notes are in

so far I've got a flow-down through Bb chord..
to F..
Quick touch back and fourth between Eb, Bb, Eb...

and then a measure of what is either an inversion of a Bb5 interval; or it's the root and 4th degree of F which is... oh sweet:
it's an F,b5 interval isn't it..?

Your last sentence has me a bit confused. The Bb5 interval you talk about makes sense (Bb and F). And it's inversion (F and Bb) as you say. Not sure what you mean by Fb5. Do you mean F and B natural?