Les,

From the dimensions you're looking for, the Parr is almost a perfect fit. Eight inches in LOA isn't going to make much of a difference. I built my son a Parr and I'm very impressed with it. It slices through the water with almost no drag whatsoever.

Some thoughts:
- The Parr is a proven design that is ready to build, you don't have to experiment with designing your own.
- The Parr moves through the water so easily, even a three year old will be able to paddle it.
- The bigger question, in my opinion, is choosing a paddle that's light enough for the little guy.
- Your grandson will grow into the Parr before you know it. If you build too small, you'll be building another one really soon.
- If you still want a shorter kayak, you could always scale the Parr down slightly. Below, I included a link to One Oean Kayaks' page on scaling.

Where do you live? I might be ready to sell my son's kayak, he seldom paddles it anyway. I'm located in Miami, FL but we could always find a way to ship it.

http://www.oneoceankayaks.com/smallwin/scale_kayak.htm