This is real simple
Every bolt has the same basic thread-engagement requirement when NO BRACKETS are used.
With every bracket that is installed, the bolt needs to be that much longer, to maintain the thread engagement.
Some bolts pass thru just one bracket, some thru two.
And if you do what I do, which is use the slanty cupped intake washers, in various spots, then you gotta add length for that as well.
When the bolts go into aluminum, be careful not to overtighten them.