Safe to put in Mercon V in A833?

I use 50/50 all year round. 50% ATF,any old ATF I got on the shelf, and 50% EP oil, 75/90.
The more ATF you use the faster the brass will want to clamp,but the longer it takes for the geartrain to slow down. And the trade-off is wear on the cluster-pin.
The more gear oil and the thicker it is, the longer it takes for the oil to get squeezed out from under the brass,but the quicker those heavy-azz gears will slow down.
So it's kindof a balancing act.
Mine shifts like lightning, but I modded it to get it to be like that,lol....Your results may vary.
I see you're in Canada too, well it almost never gets over 90*F here in southern MB,and only for about a week in July; so no big deal IMO what you run, just don't put straight 140 in it,lol. Cuz in winter the darn car won't move;you can't even tow it.
Yeah I read the FSM. I've run several different kinds of automotive oil in mine since 1970, and never had problem. In fact the current tranny is a 1965 model with all the original gears in it as far as I know. And I've been hammering on it since 2004 or so. Since mine now has over 100,000 miles on it, I'D guess the 50/50 works.
One oil I won't ever run again tho is synthetic;that stuff is just too slippery.

Oh yeah, have fun putting gear oil in there,lol