RE: proctor eindecker lll reduced to 1/6 scale scratchbuilt
6 7/8 (6.875") inch would be 17.46cm so the 18cm pot would be about 5mm over this diameter (so a bit over 2mm on the edge, which may or may not be a problem on your model). Actually, since I know I'm going to be want to use a metal cowl I usually look around for the pot first and then slightly modify the firewall to suit the pot.