K5 Help jailbreaking a K5 on 5.3.7.3

Hi,

I have a K5 on FW 5.3.7.3. I am a bit confused which JB to use because the index clearly shows my kindle should use the newer one but there is no package in the zip for it.

And the historical does have anything higher than K4..

So what am I not seeing here?

Many thanks

~michael