I've never built a kayak, or used one extensively, but...
Be aware that your widening of the hullform will have the side effect
of increasing initial stability - meaning it'll be harder to tip over.
Unfortunately, this'll also mean that it'll be harder to turn
rightside up, so make sure that you wear an appropriate lifejacket
with plenty of flotation for your size!
"In order to understand the world, one has to turn away from it on occasion..."
secure email: max c at ziplip dot com