what is the bifferent between the jdm 6bolt head and the us 6 bolt head

Nothing, other than the intake manifold. Head's themselves are identical.

absolutely nothing. Mitsu didn't do stupid jenky crap like honda and make a "better" JDM version of everything they made. Everything was the same for the most part, and whatever minute differences aren't worth going crazy for. Like the JDM 510cc injectors off the Evo3. Big whoop, evo8/9 injectors are 560cc and easier and cheaper to get. JDM evo3 cams were the same as 2G dsm cams, and for the cost, you should of got some HKS/FP/GSC/Kelford and make 30~40 more whp than that JDM crap. Bottom ends, all the same, same stroke, same bore, same compression ratio. 6 bolt bottom ends are the best stock for stock, beefy rods, and compression ratio made for high boost. Intake manifolds...Everyone says The evo3 ones are pretty good, but for the cost, it wont touch a Magnus or JMF manifold. The cyclone one is a joke, too much work and not much return. Exhaust manifold, Evo3 one is pretty good, but you can make a USDM 2G one and 1G one flow just the same with 10 minutes of porting. The collector size is the only difference physically. The actual metal is better in the 2G and Evo3 manifolds and are less prone to cracking.
JDM transmissions from the EVO3 wont work in DSM's due to a different final drive ratio. Will work if you use the Evo3 Transfercase and Rear diff too. But why? Its the same shitty weak 3 shaft design with an Input shaft, Intermediate shaft, and Output shaft with skinny gears because that all that would fit in a small case crammed with 3 shafts instead of just two. The third shaft is needed to make the Diff spin forward because our engines spin backwards. Opposite of the direction the wheels need to spin for you to drive forward.
This is how power goes from the engine to the ground:
Engine spins backwards>
Flywheel spins backwards>
Clutch Spins backwards>
Input shaft spins backwards>
Intermediate shaft spins forwards>
Output shaft (dummy shaft) spins backwards>
Diff spins forwards>
Wheels spin forwards>
Car drives forward.

Only thing good about the JDM trans from an Evo is the some of the gears inside. Mainly 5th due to it being 10% taller, so you can cruise on the freeway without being at 4K RPMs. You can do a mix and match Evo3 and DSM gears to get a close ratio trans.
Then theres the JDM galant FWD/AWD switchable trans. No, it didnt have an electronic switch. You physically have to get down under the car, take out a bolt, and move a lever on the trans and transfercase to make it switch from AWD to FWD. Don't know why you would want to be FWD for a day, but..more power to you I guess?
Transfer cases, to my knowledge, are the same other than different input/output ratios to match the trans.
Only thing good in the JDM drivetrain options is the JDM EVO3 rear diff. You have to physically take out the diff, swap the ring gear off of it and put it into your current diff housing. The JDM EVO3 Rear diff was a 4-spider Clutch type LSD unlike the USDM open 2-spider diff in some 1G's and Viscous 2-spider LSD in some 1Gs and all 2G AWD's. But no one ever really breaks a rear diff in a DSM, unless it ran dry or you make GOBS of power, in which most cases, at least for 2G guys, you break the diff cover which is what mounts the diff to the car. The actual gears inside are fine, up until the whole pumpkin smashes into the ground when it falls out.

This should be the end of all "oh shit its JDM, its mad tyte yo!!" questions/threads.