Kind of a no-go? Nope, galvanized is absolutely verboten under penalty of self inflicted death.
McMaster-Carr Supply has all the sch 80 pipe you need in iron, steel and stainless. They also have a 750° graphite based thread sealant. I measured my components with a tape measure, the same as you but be careful to allow for the dimensional reduction when one piece threads into another.
MMI and hot rod shops have the insulating wrap.
https://moyermarine.com/product/exha...exht_01-0_455/
More info
in this thread.
edit: my water injection is a custom welded fabrication so unless you have access to the necessary welding equipment for the pipe material you select, go with the
MMI injector fitting.