Wiring 4-wire Electric Range - Can I use these connectors?
If you have 3 wires coming from the wall (hot hot neutral, no ground), then you hook the wires to the 3 terminals that you see.  Note the odd little strap linking the neutral stud to the chassis of the range.  It is "grounded" to neutral.  Any fault with the neutral wire will energize the chassis at one of the hot voltages.  Yikes.  

If you have 4 wires coming from the wall (with ground), a little work is required, but this increases safety. First you remove that odd little strap, as you will be connecting neutral and ground separately.  Then you attach the ground wire to that green terminal you just removed the strap from.  That lug in your photo is a fine method to do that!  Then you connect hot-neutral-hot to the 3 studs, much like the above.  

The T&amp;B lug connectors in your question are certainly good for 40A.  UL would not let them label for #8 wire if they were not good for 40A.  They are undoubtedly a good choice for ground wire. For "hot" wires, after torquing their screw to spec, I would wrap them with shrink tubing or electrical tape.  

I agree with 'Bat that the T&amp;B connectors are a little concerning as far as hitting the chassis or something else.  That compartment doesn't apear to have a cover, and they seem awfully exposed.  See how they fit (you are sure to be able to use one) and make a judgment call.  As far as the ring terminals he is recommending, you will need larger ones that fit on #8 wire.  They do make those, but not necessarily insulated.  Then you can shrinkwrap them with shrink tubing.  Just use black.  

Uninsulated is good, though, as you can solder them with a nice large soldering iron, not the electronics pencil types but either the inductive gun type or the really big 16" long types.  For the solder, go out of your way to find old fashioned lead solder (non-RoHS; RoHS compliant unleaded solder will crystallize over 10-20 years, it is a death sentence for any eelctronics built that way). Do not use plumbing solder, it's acid core and not lead.

On a 3-wire connection, the neutral is so important that I would not trust a ring crimp terminal alone.  I would use one of the T&amp;B lug connectors, it doesn't matter if that makes contact with chassis.