The Kirk LP-70? Seems to work fine on my Flexshooter Mini too, with the lens all the way forward.The 600mm pf has potential balance issues on a normal gimbal head. The lens is more compact and weighted closer to the camera than other similar focal length lenses. When using the lens on the Z9 the balance is heavily weighted toward the camera so it has to be pushed forward quite a bit on the gimbal mount to balance properly. Adding a tc makes it even worse. You need to make sure you have a long enough foot or plate to cover the range.
I have the Kirk replacement foot and it works fine.
OP no one in this thread specified which Hejnar plate and I don't see one specific to this lens. I may have missed it.