Lube Questions

I have a new to me '64 Valiant convertible, 225 /6. Rear is leaking, I have bearings & seals on order, got capacities from an online manual. I'm in Florida, high heat.
They recommend 90 wt. for the 7 1/4" rear, yes or no?
I also have a 4speed, with a 6-14-77 date stamped on it. Recommend 140 wt., yes or no?
While we are at it Dino or synthetic?