I needed only two but like you couldn’t find any, so cut a half inch and head off a 2.5” Grade 5 bolt then die cut threads into the shank. Bit of a hassle but a good workaround.
Edit: Grade 8 bolt.
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Nice Nick, The bolts I’m getting should be 1.69" long hopefully that will be OK. I got a quote from guy at the machine shop to do the both manifolds for $ 120.00 firm price.
Probably money well spent: have him check the flatness of them, as well.
I checked they’re flat
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Longer would be better. It’s sometimes a bit of a struggle to get the downpipes, fresh donuts and flanges close enough together to expose enough thread to get the nut started, especially if you use Nordlock washers. If you run into that you can start the nuts without washers on diagonal corners then use them to pull the floating downpipe flange up high enough to apply nuts and washers to the other two, then redo the first two. Never a fun job.
It’s also a good practice, when the manifolds are off the engine, is to trial fit the donuts on the down pipes and manifolds first. I would hone out the sealing area of the manifold so the donuts would slide down into them more easily.
Thanks for the helpful comments that I can use. I have an update- I went to machinist shop 1 got a quote for $120.00, but he has bad reviews. Went to machinist shop 2 nice person wanted $140.00/hr
plus if a stud broke it would cost an additional $100.00 for each one (potential for $500.00+). So I decided to go to old timer shop the mechanic quickly pulled his tap and die sets and in no time fixed the threads and nuts,which works with hand tightening. I was very happy and asked him what do I owe you? he replied just buy me coffee, I pulled out my wallet and gave him enough for multiple coffees. Now I’m stuck with new studs and brass nuts from SNG. Case closed
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lol, I was gonna say, why not just re-thread them, but I thought that would be to crude
good on the old timer, but i expect as some material is removed in the process, relaxation of the nuts may be an issue for you to be aware of
I would use nordlocks and long manifold nuts
I use wood blocks and a jack to support and lift the ex pipe up
what are you guys using on the donut??
I use red high temp silicone
(a supposed expert mechanic on another forum was opining hi temp black works better, my ex pro uses red)
Nothing. Never a problem.
Nordlocks work well keeping the nuts tight, though they may need snugging up after a few runs, afterward won’t budge.
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I ordered the nordlocks, I use wood and jack to hold the downpipes, and red rtv .
Do you coat both sides of the donuts, the first time I only coated the back end.
The red high temp is what to use, and make sure to use the brass (bronze is better) nuts on those, not the steel ones.
like nick said, you can get ordinary long bolts, or threaded rod, amd make your own
I am so lucky to have a specialist fastener supply shop staffed with experts, I make the 30min drive a few times a year, sometimes just for one item !
So they can supply almost anything, thats where I got my silicone bronze manifold nuts
cut the tread with hacksaw is best, and dress cut threads with tiny files until they are perfect
interesting Grade 5 ?
I thought those studs are grade 8, they dont drill very easy ?
learn me up please (mine are already re-studded)
Yes, good catch. I did the job just over a week ago and the bolt head was still in the vice. The two 3/8” studs I had to replace are 1.5” and 1.625” long.
I had brass nuts on them. You can see (red arrow) where the brass thread failed. Changed over to the original spec bronze after having read a very informative post by @Roger_Payne on the subject.
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Yes I think I will. One more obstacle to go and on goes the exhaust. This is the back manifold with the crossover aluminum.
The ones I got today from SNG are 1.69" long
Should work, You want all of the nut threads engaged and some of the stud exposed after torquing.
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Just a suggestion. On my manifold downpipe studs, with the manifold out of the car I first cut a thin slit into the top of the stud, then wound it into the manifold and tightened it/them down, then with the stud/manifold held upright in the vice, spread the stud using an appropriate chisel.
I did this to prevent the stud from working loose due to heat cycles and vibration. Been this way on the car for about two years and roughly 3k miles. Good so far but probably not long enough for a “proof”.
I have frequently read that a minimum of two threads should be exposed beyond the nut for the nut to have full load capability on the bolt. On many structural steel construction projects, the engineers specify a minimum of three threads exposed beyond the nut.
The last bolt thread in the nut needs bolt length exposed to be able to transfer fully the load from the last thread in the nut to the bolt.
Of course, if the bolt and nut are not being fully loaded, not an issue, but then, what is its load rating?
Shush your dirty mouth… 
That will be someone else’s torch to carry now.
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Don’t know where I heard it but I always use 1 bolt dia length of thread sticking out.