Would you be able to post an attachment of the actual print page that you are transcribing? It seems that these are two entirely different questions, are they not? At least I don't think that m/s could be considered a fraction with opening and closing fraction indicators. Perhaps I am not understanding your question. Please clarify if necessary.
If this is a separate question, then yes, when a single-letter abbreviation is part of a fraction, the letter sign is used. See Rule VIII §51.a. where it says, "The use or non-use of the English-letter indicator with abbreviations does not depend upon the braille symbols with which the abbreviation may happen to be in contact, such as grouping symbols, braille indicators, fraction lines, the hyphen, or the slash."
See also Rule VIII §54.b with regard to spacing with abbreviations. "… A space must be left on either side of an abbreviation in all other situations." Thus in your first question the times (multiplication sign) must have a blank cell before and after, to separate it from the abbreviations kg and m.
I hope that you can follow the logic here.