First - what oil are you running? These motors are very sensitive to viscosity, and I've heard 5-30 oil make them sound like they have lifter ticks - changed for 5-20 the noise disappears.
Second - I've seen timing chains go on these motors at that mileage, though they dont really make that same noise and it tends to change with engine load. It's possible it's the injectors "clicking" - I know mine on my ranger are fairly loud and could be mistaken for top end noise if you didn't know what they sounded like. Also, dont know if these motors have spark plug issues - and if they do, don't know how this happens (meaning I dont know if they actually do come loose first or if the casting just sucks)...you may want to see if they're all tight as well.
Just some thoughts