Exhaust Stud & Flange Nuts for '99 3.8l

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I am having all sorts of problems with replacing the heads on my 1999 3.8l Mustang with the latest problem being trying to find the correct size exhaust studs & flange nuts. I ordered a set of Dorman 03133 online and got them today but they are the wrong size. It said on any website I went to that these were the correct factory replacements for all '99 - '04 3.8l engines. They are too big measuring M10-1.5 X 62mm. After removing mine I found out that they are suppose to be M8-1.25 X 62mm. Looking up for the size I need I have found them but they are for the following:
-Fits 1996-2010 Mustang 4.6
-Fits 2000 Mustang Cobra R
-Fits 2007-2010 Mustang GT500

So my main question is what kind of 3.8l engine do I have, nothing I buy seems to fit mine nor does any video I have seen on YouTube look like the engine I have. No work has ever been done on this engine other than regular maintenance since we bought it new off the showroom floor. Is it a special one of a kind engine??? Maybe a 6 banger Cobra?? J/K

Here are a couple pics, one showing the top of the engine and one showing the shorty headers or whatever you call them.

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While waiting for someone who may know the answer to my question, here's a little more info on the car itself that might help identify what engine could be in it. Since it's a '99 model, it has a "Special 35th Anniversary Edition" badge on it. I would think all '99 models would be 35th anniversary but then again maybe they made special ones with different engines, IDK?

 

[tsemmett]

All 99s are 35th Anny (Cobras did not get the fender badges though). There is an additional Limited version that was an option on GTs, but no odd engine options.

99 was the first year of that head design; maybe there were some variations? Everything I can find suggests it should have been M10x1.5.

 

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All 99s are 35th Anny (Cobras did not get the fender badges though). There is an additional Limited version that was an option on GTs, but no odd engine options.

99 was the first year of that head design; maybe there were some variations? Everything I can find suggests it should have been M10x1.5.

Thanks for that info. Do you know if all '99's came with factory shorty headers, maybe that could be why mine has the smaller studs?

 

[tsemmett]

If it has shorty headers, they're probably not factory. The ones I'm finding for factory are all like this: 3.8 Exhaust Manifolds Which do seem a touch nicer than the average manifold, but also not separate tubes to a collector like a header. Could be that someone swapped them and ended up putting thread inserts in to drop the size down. Hard to say for sure.

 

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Those are the ones I have on mine in your link which are factory since I bought mine new from the dealer. I just assumed they were called shorties also, just factory shorties. Since they are factory, then not all heads are equal because of the stud size difference.