Trans fluid

I have a saxxonette two speed with Sachs motor. I believe it’s a 1972 Arctic Cat Whisker.
would like to get it running but not sure what trans fluid to use (I heard DEX/MERC)
Also not sure what type fuel to use, would anyone have the correct information for me?
the sachs manual calls for a 25:1 ratio on gas/oil mixing, and .5 pint of sachs gear oil for the case (which can be subbed out with ATF). it's said DEX/MERC ATF is just better to use since it's an older formula for an older engine. but you can go down a rabbit hole of people debating on forums about engine oils.