Okay, I think I found it. I have the screwdriver set below and I started going through the bit "tips" that you can insert into a driver. The bit is labeled PH2. Best fit I've seen to date. These screws are soft material and can strip easily.
Above is the detail for cowl and louver screws. Only one p/n is called out on the drawing, though our process allows sizing up or down in length as required for different areas in an application like this. Generally if a longer screw is used it is usually where the top and bottom cowl overlap at the boot cowl (lower aft corner of top cowl on top of upper aft corner of bottom cowl)
The screw called out below is AN507C632R6, the last digit is the length in 16ths of an inch. so AN507C632R7 (7/16") would be the next longer, AN507C632R8 (1/2") next up after that etc.