Just Questions

IMHO mean in my humble opinion.

And yes those pictures are what is needed. Someone will come along and tell you what you need to know very shortly, I am sure.

That doesn't look like a screw, is it a plastic post ? Maybe there is a kadee specific piece to work with this. To get that out isn't all that hard.
 
Kadee also makes conversion kits to change from the truck mounted horn-hook couplers. You have to know the manufacturer of the trucks, to get the right kit. Walther's catalog has a conversion chart and you can also get it at Kadee's sight.
 
Early Bird: Lionel HO had the hook-horn or NMRA couplers like your pictures. Lionel O has their own make.
Truck mounted couplers are the hardest to change to Kadees because they're usually not designed to be replaceable, even if they break. Kadee make a #9 which has a smaller screw hole, but is otherwise like the #5. You might fit something in by trimming bits off the truck that hold the coupler.
I've been paying about $4.50 for 2 pairs of couplers, although one shop wants about $6.50 for them. (in Canada). #5s often sell for less in bulk or on sale.