>Now then, for the umpteenth time! The MB-D200 WILL fit the D300!
The MB-D200 is a Nikon battery grip. It will not fit the D300. But you probably mean the Kirk BL-D200, which is what we have been talking about so far.
So, I'll make one last attempt, not to prove whether you are right or wrong, but to try and ensure that the member originally asking the question gets an accurate answer.
Clearly, the PZ-109 is not an L-bracket. It only allows mounting of the camera on the head in landscape format. My only aim in mentioning it is that, like the BL-D200, it is carefully shaped and machined to fit exactly on a D200 baseplate.
My PZ-109 fits a D200 precisely. As I have shown with an image, it does NOT fit a D300. In order to fit a D200, I assume the mounting area of the BL-D200 must be (near enough) the same shape and profile as that of my PZ-109. This certainly looks to be the case judging from the image about 1/3 of the way down this page on the Kirk website. If it is the same, then I cannot understand how it will fit a D300. I'm certainly not saying you are lying, but something (like my PZ-109) does not quite fit
Seeing an image of your BL-D200 mounted on a D300 will help clear up this confusion. It would also illustrate whether (since the D200 and D300 bodies are a different size/shape) it is possible to open the D300's rubber connector cover with the bracket in place.