Pre1880 Bavarian Rates

I am looking for a good reference book for Bavarian postal rates during this period specifically addressing foreign rates.

I have a copy of Edwin Mueller's detailed Bavaria classic period article from the Mercury Stamp Journal (1951). While it discusses rates and is clear on the domestic and GAPU rates, it is not very informative regarding foreign letter/postcard/printed matter rates, etc.

Examples:
What was the rate to send a letter from Bavaria to England in 1871? 7kr?
Was a Correspondenz-Karte from Bavaria to England treated as a letter in 1871? 7kr?
Was Bavaria compliant with UPU rates (after July 1875) even though they were not a separate member?

Information on a concise reference regarding this period would be appreciated.

The following references may be useful.

1. Altdeutschland: die Gebühren für Brief- und Paketsendungen, Udo Durchgraf

2. Bayern Spezialkatalog Band 1, Handbuch Kreuzerausgaben, Peter Sem

3. Handbuch der Auslandstaxen der süddeutschen Postgebiete 1850-1875, Dr. Karl Zangerle

And the following two books from Literatur des Instituts für europäische Postgeschichte:

4. Bayern: die Taxbehandlung der Correspondenz nach dem Postveriensausland 1856

5. Taxbestimmungen für Briefe, Muster, Warenproben, Drucksachen und Postanweisungen nach dem Postvereins-In- und Ausland (1868)

Michel does not have a lot of information on rates to foreign countries during the Kreuzer period (to end of 1875). They do have more comprehensive information for the Pfennig period which starts in 1876.

Thank you for the references.