My span at the outside of my hands is 8 inches. I'm an tad over 6 feet, 200 plus pounds. I have big hands (XL or XXL gloves). Using the standard for my hands, my early kayaks were deeper than what I now prefer to paddle and roll. I don't think the dimensions you'd be working with are too far off the mark.
If you want to make sure the fit will be good, use the gauge with the rib-length deductions and start with a rib or two in the seat area and one near your heels. Steam and bend those into place and then set the frame right side up on the floor. Block up the frame at the height created by the ribs, hop "in" and see how you like the fit. I like to be able to do a full layback, head to the deck. If this is your first Greenland kayak, understand that your legs will be noticeably straighter than they'd be in a cruising kayak.
After your fitting you can adjust the length of the rib-length gauge.
I hope that helps.