i just got a 1999 yzf400 on trade. the guy i traded of course told me that the bike had a fresh top end... seems to be the norm for anyone trying to get rid of a bike. so naturally i didnt believe him. anyways the bike ran fine, no clacks, no grinds, shifts well, starts well, etc.. so i traded him. i was looking at the motor and there are two numbers or codes reading 52r34 and 1368 engraved on either side of the head. not the factory cast numbers either but engraved by hand. also i noticed the number 35 engraved the same way on the cam guides. does anyone know what these numbers mean if anything? could the top end or head been rebuilt at some point, not necessarily when he had it?