SSEBONNE4EVA, Yup, as far as I can see that would work just fine. BUT, that is just my opinion,, -the bigger the air space, the better I'd think. But if you use a small enough EGR tube, then "you're in business."
I had a great telephone conversation with Bill some time ago, and I know he expressed the same concern about what negative effect there might be when using the small EGR tube. I can report to everyone that I have two cars in my family now running the KenCo EGR tube, which is certainly pretty small, (-I just went out to the garage and measured the KenCo EGR tube, and actually the outside diameter is 1/2", and the inside diameter is just a touch over 3/8") And quite happily they are performing just perfectly. The '99 Bonne has run for a year now, and the '98 LaSabre has only been a few weeks.
Also, if it is any comfort, I remember someone a long time ago replied about the size of the actual passages in the EGR valve itself as being quite small. Personally, I haven't taken one of these EGR valves apart yet, but I really am curious about how small those passages probably are. If that is the case, then the 3/8" tube would be no factor at all. -I also just had the thought, that I have to suspect that maybe Ken Sprag himself had already checked into that when deciding on the size to make the tube. -just a thought.