Hey, the valve clearances seem to always tighten. I believe this is because the valve seats wear, so the valve starts to sit higher and higher up into the head and therefore closer to the cam lobes.

I've kept track of my valve clearances from 225k to now, 300k. The intake valves clearances are pretty stable. I've only had to touch 3 of 8 of them ever. The exhaust valves seem to tighten by about 1-2 thou per 60k miles. I've had to adjust all 8 exhaust valves, and one that was adjusted at 225k had to be done again at 300k (it had drifted from 12 thou to 10 thou).

With this in mind I'd shoot for the high side of center with respect to target clearances.

BTW, from what I know the 3RZ and 5VZ shims are the same...