In Germanic languages which now have 'final devoicing' (complete or incomplete), is there evidence that the contrast was realized as it is in English today?, ie in terms of robust differences in vowel duration and consonant duration?
How about asking Felicitas Kleber or Klaus Kohler about it? Judging by their publications, they should know. If there is a positive answer to your question.
Brockhaus, Wiebke. 1990. Final obstruent devoicing in German: where does it really happen? Paper given at LAGB Spring Meeting , Cambridge. Brockhaus, Wiebke. 1991. Final obstruent devoicing -why ? Paper given at LAGB Spring Meeting, Oxford. Brockhaus, Wiebke. 1992. Final Devoicing: Principles and Parameters. London: UCL Thesis.