rocker shaft cleaning ,must remove core plugs to properly clean sludge. to many on this site worey about oil return,the tubed that bleed off pressure exit into the outer drain holes Exhaust manifold side. these holes easly cleaned with oil hole brush. so when you throw away the bleed tubes and go to pressure lube the oil flow goes threw to the same aria the tubes direct, just be sure to block the holes the tubes wherein.

Meteor, properly installed overflow tubes empty into the rear pushrod hole, not the drain holes for the rocker area.  Pressurizing the rocker shafts increase the amount of oil that must exit the lower oil drain holes.

John - "The Hoosier Hurricane"

if you have a head off look at the drain holes close to exhaust side, the oil from drain tubes (via the pushrod hole comes out the same spot. if the lower drain hole is clean same amount of oil goes to oil p drive and timing chain hole .the holes at front of block 1 is lower than the other so some of the drained oil will go to the rear oil pump drive gear
in fact with drain tubes are removed and oil hole blocked less oil spills than when tubes in. this site had a good storey on proper blocking the tubes. run a 5/16 tap down the rocker stand drain hole ,take a 5/16 allen screw and grind a point on lower threaded part. this blocks the oil and positions the stand making it easeyer to install. ps the hole for the drain tube is rich size for 5/16 tap.

unless 1 removes rocker shaft core plugs ,not likly you will clean the sludge out of the shaft as it accumulates preset drain tubes