I've done this with 9/16" and with 5/8" bolts used on my current suspension....about 6 years ago, and I ain't light on my junk.
BTW: drill press "required" for accuracy....IIRC, I used grade 5 bolts and nylock nuts.
First, get a 4x4" square block of wood....drill a hole for the size bolt you plan to use (9/16" or 5/8"). Also, screw a 2x4 onto one side and drill a similar hole at the seam, then remove the 2x4...you want a trough for the bolt to lie in. Yes, the bolt will protrude thru, but that's why your drill press deck has a hole in the middle.
Now, using a spare shackle, set the side plates at the correct width, and insert the bolt thru with both bushing halves. Note that there is a gap between the bushings where you can see the bolt....this is where your grease-out hole will be located, and you want to note the depth for the center hole process.
Drop the bolt into the 4x4 hole and prep the bit with cutting oil. Carefully drill the center hole down the bolt, centering is critical, as is not going too deep. This hole can be fairly small. Then, swap to a larger bit, one sized properly for the zerk fitting to insert into. Counter-sink the existing hole sufficiently to allow the zerk to screw into it.
Then, remove the bolt and lie in the trough....you now drill another smaller hole in the side for the grease to exit, only 1/2-way thru. When you can blow air thru, you are set.
Really, it takes only a minute or so each to modify once you have the jigs set up. I've done most of mine, and have yet to have a single problem.
Still not convinced it makes a noticeable difference in the suspension, but it doesn't hurt anything.