Great to know the cap fits DESW! When I get time (likely after summer), I'll see about designing another cap that can mount the Snowspeeder that comes in the Hot Wheels set with the AT-AT and upload to Thingiverse for printing. Then you can print out a combination of AT-ATs and Snowspeeders to fill out the four PB caps.
Based on the photos - it looks like I'll have to design a mount for the Snowspeeder on the mid-left cap to jut out away from the wireform above. And the cap screws are E/W and not N/S on a stock machine, right?