The gen 1 motor will work fine in the gen 2. Use all of the gen 2 computers. ECU PCM etc.
The spin on oil filter can be swapped over. The gen 2 valve cover should be swapped over as it is a better design and helps with crankcase ventilation.
Your issue might be more that a lot of the JDM...
is that just a replacement center section for the axles? so you just rebuild the explorer ones and are good to go? thats pretty slick if that is the case
So they probably don't need to be in the best condition to do their job in that location. But at that price if you can press them in and put yourself might as well change them while they are out
There is no factory cold air. There was a dealer installed AEM intake that was Mazdaspeed branded for the first gen. If this is what you have its junk pick up a short ram sri from corksport during the sale they have going on now and throw the cai out. Turbo timer is also more trouble than it is...