You can buy a tool called a clickadjust, this accounts for the MASSIVE wear these suffer from.
A alloy RC will be the best thing for noise.
You can also take the rocker gear apart, then turn the rocker shaft(180) so the left becomes right, and right becomes left, then ROTATE 180 degrees, then rebuild.
This puts the UN worn face lower most where the load is, done it loads of times.
When adjusting the clearances pull the rocker arm up to try to get any wear in it accounted for and adjust whilst still holding, running the valves closer will kill the performance, a slightly larger gap on the exhaust helps sometimes on these depending on how wild the cam is.
tabetha