The stock Toyota shackles are extremely hardened so drilling while possible is going to be a bit of a chore and could in fact introduce more failure points than it solves. If you haven't felt the need to have greaseable for the last 11 years perhaps stick with the stock setup? The other hitch on the bushings is the different diameter for greasable versus non. OME makes a set of bushings only for use with the stock shackles and they may not have the gap in between the two bushings to provide a place for the grease to go. I've honestly never measured as I've not tried to go the direction you are. Assuming your comfortable with the drilling/tapping and the bushings will work or can be easily remedied, I say go for it.
Old Man Emu is currently back-ordered on one of the rear springs and have been for about a month now, I'm not in front of my work goods so I'm not sure if there has been an update but they didn't even have a current ETA for their next batch as of several weeks ago. So at that, start checking around with some of the reputable companies in the west and hopefully someone has a kit in stock. Good luck!
