Couple things to consider with stock adjustable rockers. First, notice the oiling holes that squirt pressurized oil on the valve tip on one side and on the adjuster on the backside. If the rockers have too much slop in their bore, oil leakage will drop oil pressure overall and the valve tip and pushrod will not get proper cooling lube.
Second, if you keep the factory adjusters, make sure they are super tight, or they could loosen with use. They rely only on the interference fit of the threads. If they've been adjusted multiple times in the past, they may have provided their own, happier threads.
Third, if you use the stock rockers and change to aftermarket adjusters, that will completely negate the chance of loosening, but the rockers must be machined to do so. The stock rocker does not have a flat surface for the locking nut to locate on. Instead, it will bottom on the highest point, loading the adjuster unevenly. Broken adjusters or rockers could result.
Lastly, if you do go the route of aftermarket adjusters, make sure you buy pushrods of a length that allow the adjuster to be lowered just enough to allow the oil hole to squirt above the cup. Otherwise, the cups will not be getting proper lube, instead, they shield themselves.
On that last note, not everyone agrees with me on that and they suggest you need to crank the adjuster up as high as possible for proper geometry. He'll be along any minute to explain himself. I stand by the words I've written above.
