SEE THE PIC BELOW FOR ALL THE DIMENSIONS THE HEADS WE SELL THAT WORK WITH THIS PISTON KIT ARE LISTED AT THE BOTTOM OF THIS PAGE, SCROLL DOWN PLEASE. THIS WORKS ON TRX90'S THAT HAVE "BIG_DOME" OR "OLD_70_DOME" HEADS HEADS FROM THE FOLLOWING WILL WORK GREAT: OUR OLD_STYLE ULTRA_HEAD WITH_RACE_CAM (OLD_70_DOME) 25MM_INTAKE 22MM_EXHAUST OR XR/CRF50/70 RACE HEADS WITH 22MM AND 25MM VALVES. CT70_K0_TO_1977 ATC70_ALL ALL_SL70 ALL_XL70 ALL_CL70 C70M_1970/71 54MM HI_COMPRESSION RACING_PISTON (12:1/or_more) 13MM_PIN TRX90_114CC (54/GBO) 54/GBO$39.95 CLICK ON PICTURE ONCE THEN AGAIN FOR DIMENSIONS CLICK ON PICTURE ONCE THEN AGAIN CLICK ON PICTURE ONCE THEN AGAIN CLICK ON PICTURE ONCE THEN AGAIN CLICK ON PICTURE ONCE THEN AGAIN CLICK ON PICTURE ONCE THEN AGAIN HEAD_DOME'S_? RODS_LONG/SHORT_? WHICH_DO_I_HAVE_? THESE ARE THE AREA'S TO BE TRIMMED FOR THE 54MM CYLINDER MUST REMOVE SOME ALUMINUM HERE FOR 54MM CYLINDER MAKE SURE TO SLIDE CYL. DOWN STUDS TO CHECK FOR CLEARANCE SLIDE BARE CYLINDER DOWN STUDS AND MAKE SURE ALL IS FLUSH