The length of the shanks on all open-end or close-end wrenches is designed and made that way to get the correct torque without the need to measure it with a torque wrench. This is why a 7/16" wrench is so much shorter in length than the open end wrench for 3/4" nuts.
If I can't find what torque I need, I measure the size of the threads. I seem to remember that the two studs for the rocker cover are 5/16" UNF threads. Then I go to see what the torque is listed for another bolt on the TR where the thread size is the same.
To keep oil from leaking out all around the nuts which secure the rocker cover in place, I use a fiber washer and a flat washer under each nyloc nut. In both cases, I selected washers for 1/4" bolts and hand filed the center holes with a round file so they would be an exact fit when I drop them onto the studs, and then I tighten down the nut. Since the holes in the washers (especially the fiber washers) are so exactly to size, I rarely see any oil around these studs on top of my rocker cover.