Huh, thought they were studs. Why do the head gaskets fail so often? I always assumed it was a problem with the head gasket bolts stretching through heat cycles.
[Me on a pulpit..
]
Toyota had problems initially with the loss of asbestos type gaskets, and initially what looked to be improper procedure in torque with the MLS type, thus the recall. It's a pretty well known issue, but compare it to other makes, specifically domestics and look at the life span of the engines, Toyota and Honda rule, period.
From what I have personally seen and experienced, the bolts don't stretch any more than the initial torque procedure causes. It comes down to torque and prep. The one above we're redoing had over 260k on it before it became an issue, and mine was because, well, it was an overheated transmission and engine and, honestly in my case, 2wd-Auto, 3VZE, 600-700 lbs of gear and a 6-7 hour trip in 90 degree heat at a constant 65mph will kill almost anything, regardless of stopping a couple times for gas.
In other words, I beat up on it a lot, and why I went through everything and swapped to a manual 5 speed 4wd.
They have had similar issues with the 3.4, aside from the upside down gasket issue and IIRC have also bumped up the head bolt torque from 25 ft/lbs to 27 or so.
(*It is just not something Toyota took to a public service campaign, I saw this in a tech notice only I was shown, that is an in-house printout customers and others don't necessarily always see.)
I've seen these engines go well over 300k mi before finally giving up the ghost, even then, they only needed to be over bored by .02 (20 thousandths) and are working in the owners vehicles still with no further signs of the issue.
Now add in this contributing factor, the walking piston rings. Some engines experience this around 235-275k mi. It is another thing people rarely find out about, as it's easier to explain as a "Bad head gasket" since you're in there anyhow.
~All rings walk, I have seen 3 engines in no specific cylinder location, have the rings so gummed up and aligned that they were allowing the compression loss. As in, yes, all the slots aligned up, top to bottom, and barely 15 psi and falling.
People insult the little 3VZE to readily. Yeah the 3.4's nice, but expensive to swap to.
[End Semi-Off-Topic Sermon.]
*Feel free to throw this all back at me if these two go bad in the next 20-30k b/c of the gaskets, it'll be my bad.
No matter which way I turned it! 
