Yes, 60 and 40 thirds are interchangeable.
You can take the discs from a 60 and bolt it onto a 40 axle. You have to swap everything from the trunion bearings out, including the birfield. Some of the older 40 axles have smaller opening on the axle end, so you have to grind the ball a little so that the birf will slide into the housing.
40 and 60 axles by themselves are only marginally stronger. The axle shafts are the same strength, the pinion (if it is fine spline like the 60 and later 40) is the same diameter as a mini pinion, the birfs are the same (late 40, 60 and mini). The LC ring gear is bigger, so there is some strength advantage there.
The 82 should be 4.10. I would look on 4x4wire.com in the toyota section, it will confirm that. There were some 4.30 ratios in a certain year minis and I can't remember whether it is the 81 or 82 year model.
What are you planning?
Jack