from the "BACK IN THE DAY" file : let's see if I can get this right .

I believe it was mid 1972 when the change over to Lenco's started.At the time 833 was being used by all the GM cars and breakage was not the primary
reason most teams changed. It was the reducton in ET for the average driver. Most gained well over a tenth. Most except Ronnie Sox who actually ran slower with one.
The Pro Stock cars were in the 9.0 Et range and at 3000lbs .That converts to about 77HP.
9,000 RPM launches were common.
In today's world with slipper type clutches I think they could handle more than that