Before this mod turns into the end-all fix for whatever ails your motor, remember these jets are all about piston cooling and it will probably only serve those who are turboing or SC'ing their 1UZ. If you're staying NA, there's not much need for this.
Regarding mounting and sealing these squirters, if there's not enough meat in that web to get at least five threads well anchored, then it's time to weld bosses into the web for these to mount to. I can't imagine anything much worse than installing these to protect the pistons, then destroying the motor when one of them comes loose and starts banging around.
Maybe one reason Lexus didn't provide squirters on the 1UZ or 3UZ blocks is that the web is just too thin for good anchoring. And these blocks are aluminum, whereas the 2UZ blocks are cast iron, and there's less chance of these pulling, or vibrating out. Hmmm, maybe bosses AND helicoils wouldn't be a bad idea :veryhappy
Let's see what David has to say about the thickness of the block in that area....
John