im finishing up the whole swap from a 2000 explorer.
get a nice cam, valve springs and seals. get and intake elbow or do the fox TB conversion. BBK longtubes w/ extensions and a mid pipe. Transfer the oil system and pan from your car. bolt up accessory's. 90 deg universal V8 wires. There is an oil elbow that is on the explorer block, i left it on and works fine for clearance... i don't have AC so i don't know if you keep it if it will fit, i still think it would to be honest.
You can read up on cobra cams that make good power, the one in my sig idles great even with an auto, then again i have my car tuned. If you don't want to tune it you can buy a stock cobra cam/rockers or use your stock cam from the GT... not really recommended.
A new upper/lower intake is do-able too for more power, up to you.