Hi Jim. First of all, let me publicaly thank you for that free wonderful little collection of 1c admirals you gave away in the draw of names in September. Appreciated!

As to your question, I have an extra german manufacturers mount gauge, Leuchterum/Lighthouse I believe, and I can mail to you. Just email me your address.
Personally, if you are using preprinted pages it is recommended to go with clear mounts so the image or number is still viewable when the stamps are removed. If you want to highlight the stamps on blank pages or mount on pages for shows I would recommend the black mounts. These tend to highlight the border and perforations more and lighter colored stamps.
As to back split or open top, I recommend the split back. With open tops, if for any reason your album or pages get bumped or turned upside down the stamps will shift, usually falling out of the mount. The same thing as what happens with stockbooks. Strips are great as you can cut them with a mount cutter to the size desired and are more economical than precut mounts. Price is always a big determining factor but preference still ultimately falls with the user.
Pretty well all mounts being quite similar, with most produced in Germany, today come with a moisture activated adhesive affixed to the mount. Use a very small amount of moistue across the middle of the top of the mount only to allow it to remain flexable enough to mount your stamps. As well this will prevent unnecessary wrinkling of the album page when the gum dries and shrinks.
Sorry I don't have it in front of me where I am now to check on the size for Jubs.
Mike