That's the original 1930s Queensway tunnel which feeds, as you have found, into the A41,
Indeed. Back in the day my father used to take the A41 all the way down to London.
Many sections south of Birmingham were derated when the M40 was opened and a few years back I followed the old A41 (now mostly the B4100 north of Bicester) just to see what it was now like. I rejoined modern life when we hit the M42 as I didn't fancy braving Birmingham and its surroundings.