In this week's Aircraft Spruce shipment I received the proper nuts to go on the bolts that secure the gearlegs to the engine mount, so on they went:
The plans call for regular AN365 nyloc nuts here, but I've already decided to use only all-metal locknuts forward of the firewall, no exceptions. AC43.13 only forbids nylon nuts where temperatures exceed 250°F, but since I'm not in a position to measure peak temperatures in various locations forward of the firewall, I'd rather just outlaw nylocs entirely.