Yes, I know the spelling is not modern German. "Ganczen" is what I found when searching through Google.

Actually, we don't know whether the original was even German (Deutsch). In the 15th Century there could have been a Germanic language where "ganczen" was the standard spelling.

I see that some sources have ganczen and some have ganczem. Hmmm

Mostly I was hoping that someone Germany, Austria, or other German-speaking area would be familiar with the song.