The roller rockers have more ratio than the stockers...that will produce more total lift. But V-P clearance on a Nailhead is tightest near TDC when the exhaust is closing and the intake is opening....the extra ratio of the rockers will affect v-p clearance only about 0.020" with a stock cam.... really not too significant.
If you install a cam with a lot more duration, or tighter lobe centers, you'll have to check v-p clearance.
Rumor has it the TA roller rockers won't fit under the BUICK alum valve covers. And I believe they oil differently..... thru the pushrods instead of thru the shafts....requiring extra cost pushrods.
Best to contact TA and Tom Telesco to compare the two available versions of the roller rockers.
I'm using Tom's rockers on new shafts and reusing the stock stands, spacer springs and pushrods.....with excellent results.