The biggest issue with bushings on the shaft is getting enough oil at the shafts with enough pressure to lube the bushing. You aren't going to run 20-30 pounds of hot idle oil pressure and keep the rockers off the shafts.
The Jesel’s use a small solid shaft for each pair of rockers, and have no internal oiling provisions.
Without creating an internal oil circuit to connect the oil supply from the pushrod to the inside of the rocker bore, it wouldn’t matter how much oil pressure there is....... the only oil getting to the bushing is what manages to leak in between the shaft and bushing via splash.
