I'm getting ready to install some log style cast aluminum exhaust manifolds on my brand new 6.2 LS aluminum heads. Sure would like to do it right the first time. Flange is 18 t0 20 mm (.70 inch ) thick. Any recommendations??

Any grade 5 bolts would be fine with whatever head works best for you. 6 pt, 12 pt, or Allen head.

I’m a fan of ARP bolts for sure. Look up the site and see what they have to meet your specs. Stay clear of any local hardware store bolts. Most but not all of them are not up to the task and are Chineseium.

I would also go with ARP if they have something. The bolts should be 8mm x 1.25 You might want to think about using studs instead of bolts. Get them long enough to get almost full depth thread engagement in the head. It looks like their LS stud kit (434-1301) is made for a 3/8" flange so you will probably need something longer. Their tech line has always been very helpful. I would call them and see what they have.

I like the idea of the ARP bolts and will give them a call this week. Having read so many posts of fighting broken exhaust bolts in the head, you can't help but wonder if anyone has found a really good solution. Thanks again!

I too like the idea of studs, makes the installation much easier. What's the consensus/opinion on using anti-seize on the threads, either bolts or studs?

Cadmium plated bolts/studs would be corrosion resistant and they get along well with alum.

Take a look at pages 92 and 93

https://arpcatalog.com/92/

I use the black socket head cap screws grade 5 or 8. I found these to be the easiest assemble and remove with extensions and ball end Allen wrenches. I have to do less contorting with body, arms and hands in the bilge. Also I use a small amount of anti seize.

Ayuh,..... Whatever bolts/ studs you decide on,... Coat the threads, 'n exposed aluminum contact areas/ surfaces with quicksilver perfect seal 1st,....

They'll come apart easier when you need to take 'em apart,....