It's 1/4-20. Measure your bosses and add 1/2" for the OAL.
The way to tell if you need SAE or metric is to look at what the bolt threads into. If it's a turbo specific part like an intake, crank pulley, accessory bracket, etc it'll be metric. If the threads into a plain ole shitbox 3.8 N/A part, it's SAE. Like anything to bolt to the heads or block.
The only exceptions are that goofy useless stud bolt on the water pump. It's metric. And the bolt that hold the accessory bracket to the block and head are metric.
You have to pay attention on some assemblies too. Some have both... Like the crank hub. The bolts that hold the pulley to the hub are metric, the hub to balancer bolts are SAE. Headers are the same way, X-over bolts are metric.
With my header bolt kit, all the header stuff is SAE but on the factory setup the studs have SAE ends and Metric ends (much like the factory bolts on the bottom of the timing cover).