Are the timing keys for the GX390 the same as the GX200? On the NR site, they seem to be the same "Key, Timing, Offset, GX Hondas, 6.5 to 15 hp Chinese OHV, & Predator" but everywhere else it seems they only list them for GX200 and other 6.5 clones.
http://www.nrracing.com/product-p/nrkey.htm