The only difference between the K1 and the K1mkII is the internal motherboard. Pentax had an exchange program where they would swap out the motherboard thereby upgrading the K1 to the K1mkII for $500. There are no external physical body differences.
In the past I had used Kirk L brackets and liked them a lot. With the K1, I compared images of the L brackets from both Kirk and RRS. I went with the RRS L bracket because it fit a bit snugger to the body. I've had it now for 4 years and no complaints.
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Here is the review of the mkII - First paragraph and image indicates all the changes are internal.
Last edited by interested_observer; 10-02-2020 at 10:13 PM.