We messed with the exhaust today, put a muffler delete and custom tailpipe on it. No big deal.

Though my family pointed out that the orange ring of gasket maker between oil pan and engine block indicates something. Not to mention it has 195000 miles on it.

This is the part where I'm starting to think I don't have a stock engine.
195000 miles should not go 0-60 in 9-10 seconds. Which brand new the 99 3.8l mustang 8-9 seconds from 0-60. So overall it has a good chunk of power. I say rebuilt recently within 100000 miles, but I could be wrong. Well after I put just a straight tailpipe on there no tips or anything. My dad mention something of it sounding like a 4.3l? Yes you can bore out a 3.8 to 4.3 in this engine. Which I won't deny its be pretty awesome. Any how I also get a whooping 20 mpg city up to 27 highway.. the standard for this car is 17 city/25 highway. Yeah big difference. I know a lot of people say bigger the engine worse the gas. Wrong, I've drove a 89 Chevy with a 400 small block that got a whooping 22 mpg combined. Its just matter of physics.
I have a 99 ford mustang 3.8L V6 with a 4 auto w/overdrive.

Now to the pointers:
Orange gasket maker at bottom of the engine.
Louder than a normal 3.8L before muffler delete.
My heads have a sticker on the that say "Green State 530".
Heads have a worn out sticker that say "Engine NIND3AR"
0-60 = 9.5 seconds (not flooring it)
0-70 = 11.4 seconds (not flooring it)
I also have a external punch of a roman numeral 1 on my engine block.

No I do not have a a machine to test torque and hp.

So can anyone tell me if I have a stock engine or not?
Perhaps give me the serial numbers location to see if is?