27 foot seems big for non scissor jack. My 20ft has four of the C-type stabs, like your pictures. When I deploy all four, I have no side to side stability issues.
I normally use no bracing or supplemental timbers under my jacks. I have the add-on stab feet, and that's all I use. My trailer sits so low to the ground, it's only a few inches before they make contact.
What material are you parking on? When I'm on anything but concrete, I give the jacks 1/2 turn or so after they make contact, to compress the ground under them a bit.
Go for scissor jacks if you have the ground clearance, they're a lot taller than the c jack. Personally I would avoid Harbor Freight jacks, you want quality steel and quality paint on these, or they'll rust solid like the junk that KZ originally equipped my trailer with (in just three years.)
