I've done the valve cover gaskets and replaced the knock sensors. Other than 3 timing belt jobs that's about all the engine-ish-invasive things I've done to it.
Back when I bought it at 119,666 miles in '05 I called and checked on recalls done or pending- Toyota said only the rear spring recall was done. There is an unreadable recall tag on the truck. There's nothing engine related in the receipts I received. Doesn't mean it wasn't done, though.
I believe there were 3 head gasket versions and this definitely is not the last one, but I don't know the difference between the earlier ones. Nothing I haven't taken apart looks to have been taken apart, but after almost a couple hundred thousand miles who knows?
Given the state of #4 and #6 if #3 hadn't failed it was only a matter of time before I'd be doing head gaskets anyway. So glad it failed now instead of in the middle of winter!