English Patriot
In spite of your obvious frustration with the feedback given by Brian and Eric, it would probably be of substantial benefit to you if you would "step back" emotionally and listen to what they and others are telling you. To use the Kirk D200 L-Plate on a D300 can cause a number of problems with not only the quality of your photography, but also possibly cause severe damage to your D300.

From a photographic image perspective, the orientation of the L-Plate on the camera body is critical to proper alignment for a number of applications, with one particular example being landscape panoramas. In this and many other applications, the L-Plate is an integral part of an entire system including the tripod, head, camera rotation device, nodal slide plate, etc. If the L-Plate doesn't align exactly with the camera base, the rotation of the camera on the panorama support system will not be correct, resulting in mis-alignment of the images. This will most likely produce inferior results when you attempt to stitch them together, whether manually or even with sophisticated software. There are many other situations where this is a critical issue as well.

And from an engineering/mechanical perspective, if you are using the incorrect L-Plate on a DSLR, particularly one that creates a gap between the plate and camera base, there is a substantial potential for the constant torque created by the tripod connection screw to distort the camera base, and could in fact pull the screw mount out of the camera base. To work properly the L-Plate is engineered to fit flat against the camera base to distribute the load properly. If it's mis-aligned, you're asking for problems.

Please note that I speak from substantial experience with Arca Swiss style equipment including a wide variety of lens and camera body plates by Arca Swiss, Wimberly, Kirk and RRS, as well as lots of other Arca Swiss style support equipment. And I own both the D200 and D300 as well as their "correctly designed" individual L-Plates. As an "old Indiana boy", I also was acquainted with the originator of Kirk Enterprises long ago when he first started up in Angola IN. His company has always been concerned with providing the best possible "correctly engineered" products to the photographic industry, at competitive prices. If the Kirk engineers thought the BL-D200 L-Plate would properly fit the D300, they would have marketed it as such. But they knew it wouldn't and had to create a new one in the BL-D300 L-Plate.

As an example of this philosophy, note that they market the same BL-D300G L-Plate for the MB-D10 grip for both the D300 and the D700, but have designed a new BL-D700 L-Plate for the D700 body without the grip. Here's the link to their website for these:

http://www.kirkphoto.com/lbracketsn.html

Even very small changes in camera body design require entirely new accessory equipment like L-Plates to fully function properly. While you can do whatever you wish with your BL-D200 and D300 body, it is a total misstatement to say, per your quotes "The Kirk D200 "L" Bracket DOES fit the D300, I have one fitted!", and "The Kirk L Bracket D200 fits on the D300 very securely" When you're dealing with custom designed photographic equipment like this, the word "fit" has the connotation of "fitting correctly from an engineering perspective". Clearly, the BL-D200 L-Plate does not correctly fit the D300.

Experienced photographers and long time members of Nikonians.org like Brian and Eric know that it's important to disseminate the most accurate information possible to those asking questions on this forum, since it can have a substantial negative financial impact if it's wrong. That's why they went to such lengths to attempt to clarify your posting information. And frankly, IMO, Brian's patience with this post borders on that of "sainthood"!!!

OldPhotos
"If everyone possesses some measure of this intangible quality called creativity, photography is unprecedented as an outlet for its expression." - Ansel Adams