Early on in the build of my Yost Sea Cruiser, I was alerted to the possibility of insufficient leg or shin or foot room by a multi-chine Sea Rider builder in NZ who was about 1 step ahead of me at the time. So I left lots of “meat” above the cutout of frame #2 and the 'masik' frame #3 to allow for possible modification.

With the frame part-built, I did a trial “slide-in to the cockpit” check to find that my shins hit frame 3 on the way in and there was not sufficient room.

Whilst keeping Tom's Offset Points – the just visible nail holes - per plan, my solution was to revise the cut-out shape from straight lines to generous pencil curves and to then cut the top curve of the frames such that Tom's suggested frame depth of approx 26 to 28mm (if memory serves correctly 2 years after the build).

This worked out fine for 6' 1” me with Aust size 10.5 feet.
My NZ friend had a bigger problem with a fused ankle joint and after a 'fit trial' he had to made a new 'masik' frame 75mm (3”) taller and the next frame forward about 1 3/4” taller.
Regarding foot rests, I made mine from scraps of WRC and plywood but used the same 14 1/2" centres as the Yakima, SeaLect and Smart Track commercial footbrace just in case. Mine weighed 1.7kg each; the commercial ones weighed 4.7kg each - a huge weight saving of 6kg in the finished craft. I paddle with my heels touching, feet splayed out at about 20 degrees and bootie toes touching the underside of the skin.

Good luck with your build.