KAE exhaust manifold bolt length?

[ReaperBJJ]

Looking through the engine bay of my project 240 I noticed that the previous owner had way too long of bolts on the exhaust manifold and oversized hex nuts and washers to fill the gap. I definitely what to replace this because while the engine is on you can hear all the nuts and washers chattering a bit. The bolt size looks like it's 10-12mm but I'd like to know what the correct length of the bolt should be.