webco made them for 250 and 360 & 400 cc yamahas. T&M made them for 250's, DG made them for RM 500 and CR 480 and CR 250's plus theres more!. i initially thought there wasnt much in the way of heads for bikes over 175 but when i did more research i found out that wasnt true
but yes ive never seen on know of one for a RM 400