Here is an image from the Machzor of Worms (from the 13th century) with Kal rather than Kol:
However, please consider that it is written in a hodgepodge of Hebrew and Aramaic. Do you think that the word מיום כיפורים זה and הבא עלינו לטובה or שבועות are Aramaic?
Ultimately, as long as we have the correct intent and are saying what has been established as a nusach, I cannot really see myself bothered one way or the other.
An additional point. In Daniel, which contains Biblical Aramaic, we see kol. Thus, in Daniel 4:3:
וּמִנִּי, שִׂים טְעֵם, לְהַנְעָלָה קָדָמַי, לְכֹל חַכִּימֵי בָבֶל: דִּי-פְשַׁר חֶלְמָא, יְהוֹדְעֻנַּנִי.
However, two pesukim later, with a makef introduced, we have kal:
בֵּלְטְשַׁאצַּר, רַב חַרְטֻמַּיָּא--דִּי אֲנָה יִדְעֵת דִּי רוּחַ אֱלָהִין קַדִּישִׁין בָּךְ, וְכָל-רָז לָא-אָנֵס לָךְ; חֶזְוֵי חֶלְמִי דִי-חֲזֵית וּפִשְׁרֵהּ, אֱמַר.
If we trust the Masoretes for their vocalization of Aramaic, then this would should that there is indeed Kol in Aramaic. Which in turn would undermine the entire premise of the question.
By the way, at least in Hebrew, the kamatz of kal is a kamatz katan, pronounced almost like or identical to a cholam. In which case, there would not really be much a difference. Would this extend to Aramaic? Maybe not.