Seat and Foot well Dimensions - Conversion

I paddle on the Bay of Fundy, Canada.
I'm interested in converting one of these...
www.seaknife.com/fierce.htm

It's 16.5' long and 23.5" wide, and paddles well, but the hatches and cockpit coaming are crap anyway, and I got it cheap. I really like the idea of being able to dress for the water without overheating, and wet exits and re-entries especially when there are lots of rocks about. We don't get really big surf here, but we do have really big tides, and really big rocks. Surface temp varies from 2degC in March to 12degC in September. No, I don't do winter storms. Strictly sunny harbour paddles in winter, but I hope to get into longer open water paddles in summer.

I saw the Hayes Homebuilt page,
www.surfski.info/content/view/650/147/
which was very inspirational, and so I'm using that as a guideline. Basically I'm grinding off the deck completely, and adding a Hayes Homebuilt wood/epoxy deck. Any suggestions on dimensions, or should I just measure myself? I'm most curious about how wide apart my heels and knees should be, and what angle my knees should be net. Any ideas would be greatly appreciated.

For those curious, what I do currently is I've added foam on the inside cockpit, and I re-enter after a wet exit by climbing up belly down from the side stern quarter, and pull myself up with both legs spread wide, then flip up and fall in butt first, still dangling feet in water. The extra foam eliminates the free-surface effect. By converting it to a surf-ski I will have even less bailing to do, and can reduce the freeboard a little also. I developed this approach more or less as a habit from laser sailing. It is re-assuring that surf-ski paddlers do something very similar.

p.s. I will also be adding a skeg or rudder, so I'll check on those topics. It tracks really well, and steers well enough, but doesn't handle well downwind in waves. A skeg or rudder should fix that.

p.p.s. I might go super long and skinny later, but 16.5' and 23" is good for now.

Seriously, having been down this road, don't do it. Try get hold of a used surfski - there must be one or 2 in Canada or east coast US. Start with a Fenn XT or similar and good luck.