I have UK Size 12 feet (US 13) and I'm about 6ft. Probably just on 6ft but I don't think I've over.
I had my boat set up with my weight well balanced in the middle. I had plenty of room. I then moved the seat at least 1inch forward I'd say? maybe more I'm not sure but it was a bit. The boat is now unbalanced and I have too much weight forward (I only moved it forward to muck around in the flat a bit). I don't feel too tight in the boat and am still comfortable. I think I could go even further forward if I wanted (I don't, I really need to go further back). So I'd say, assuming your body was the same ratio as mine (e.g. u don't have extra long legs or something) that if you're about 2" taller, maybe only 1" would be in the legs? which in my view would mean you'd still have plenty of room.
The only thing I suggest when setting up the happy feet system in the jackson kayaks is to set it up last. Maybe take it out, sit in the boat and get the seat where you want, and where ur feet can be comfortable with nothing in it. Then after that put the happy feet back in and make them fit to how you were without them. I've re-done my happy feet a few times because I thought I didn't have much room (due to just having all the beans in a bad spot) but if I take them out and realise how much room I actually have in the boat then just spend 5mins or so getting the happy feet comfortable and to just fill the void and not take up uncessacary space, everything is sweet!