Strictly speaking, can adjacent voices (aside from tenor and bass) be an octave apart from each other? They can't be more than an octave apart but is it a violation of principle to make them an octave apart?
In traditional four-part harmony, adjacent voices may be up to a major-tenth apart at the widest possible range. It is preferential for them to remain an octave or less in distance, but octaves themselves are perfectly acceptable. The Tenor and Bass voice may be up to a perfect-twelfth part, though Bach certainly has broken this rule.
There are some Bach chorales that I have played where there was a 2 1/2 octave split between the Bass and Tenor voices.