during the guitar solo, Brian plays an altered scale - slide riff during the solo (measure 47-48). Is this a turn around on the V chord, the bass drops out? The chord progression picks back up after this 2 measure break.

I would include a pic of the staff line if I knew how to add a photo.

Quote by gravitycure
The bass drops out entirely during this measure.

Dropping the bass also a typical gesture on the dominant. Song is a short repeating form, so just listen what the bass is doing during the same part in other verses.

If I recall, the whole song is just an descending minor bass line, so if the last note before the break is bVI, well, there's pretty much only one option. I know the song doesn't launch into an unrelated key.