The FT is uncommon compared to the FTn. I have the Ftn repair manual, but cannot find an FT repair manual.
I think if you check the viewfinder coverage for the Nikkormat series- will give as good an indication that the Prism is the same. The FT covers 92% of the frame, same as the FTn, FT2, and FT3.
The Nikkormat EL Also covers 92% of the frame. Same logic- probably compatible prism.
On a humorous note: The prism of the Minolta XG-1 fits in the Kodak Retina Reflex-S perfectly, and is much brighter than the original. Cameras made decades apart, half-way around the world apart. You never know until you take the cameras apart and try it out. I still have the Retina Reflex-S, brightest Viewfinder of any of them.