rocker arm shaft

FWIW...... I checked some 273 adjustable rocker shafts with banana grooves versus stamped rocker shafts, and the oiling holes in the adjustable banana groove shafts were significantly smaller but there are 2 per rocker so the total flow area is the same.

Banana grooving is just a groove that you could put in with an air cut-off wheel in any shaft. Long, narrow, tapered at the ends, and shallow, with the oil hole in the center, used to just spread the oil across the adjustable rockers' bores.