Peter, it's your build, and ultimately, your plane, but in my opinion, Randy is right. He's basing his remarks from the experiences of Ted Fancher discovering that he had to close up all those cowl outlets on his Trivial Pursuit, because they were allowing the heated pressurized air inside the cowl area to escape before it reached far enough back to cool the header, and the pipe. Ted experienced run problems before he figured it out, and closing the outlets cured them handily, as I recall.
Yes, you could install some small electric fans. Neat as that seems, wouldn't that be making the problem of cooling the power system more complex? There is a proven method that requires no additional energy, works great when the plane is under power, and shuts down when the power does. Both Randy, and now, myself are advocating you consider using it. Of course, it's ultimately your choice.
Speaking of cooling issues, at one time I felt that cooling outlets designed to get cool air to the crankcase would be beneficial. I set up the Legacy I was then building to extract air from the crankcase area. After many many flights, I've come to the realization that crankcase over heating is probably a non-issue.
As I've found out, the air entering the crankcase through the venturii is cooler than the upper part of the engine. This naturally cools the lower end, when the engine is running. The heat is created at the top of the cylinder, and at the exhaust, making these areas the most important to have adequate cooling.
I've also found that the spinner is usually cool right after the engine shuts down. It does heat up as it acts similarly to a heat sink, but the heat reaches a peak, to match the engine, then drops as the engine cools down.
In my experience with this design, the Pathfinder L.E., the cooling air should not be allowed to escape the cowl and tunnel, until after the rear manifold, and coupler when using a pipe.
I also took my version of the prototype down, and took some pictures of the cowl, and the mounting so you can see how the dowels are used at the Front of the cowl. This set up has proven out to be very secure on the prototypes.
Your build is moving along at a good pace, and looks good. I'm looking forward to future installments, and the finishing and trimming flights.