<p>Back in the day, I had two Nikon F's. One was a '68 with std. prism and the other a '72 with the FTn meter prism. On the '72 the lower corners were milled out so the clamping pins could secure it. If you notice the small lever on the front of the FTn prism, it will flex the lower clamping pins in and out. So when you slide the FTn prism on the spring loaded pins just clamped on to the lower nameplate, and to remove it you pushed in the small lever on the front, along with pushing the button on the rear of the body to release the prism. I'm not sure, but there might have been some differences on the side of the nameplate also. You definitely have to replace the name plate for the FTn prism to mount on a '68 F body.</p>
<p>I hope this helps,<br>
Ron</p>