91 2.3l Exhaust And Intake Questions.

Check your exhaust manifold for cracks.. it's common and robs allot of power. If so do the Ranger header swap. I did used a 93 header to replace the badly cracked stock manifold on mine and it made a big different. Not only does it weight twenty pounds less (26lbs vs 6lbs) but it also made a noticeable difference in throttle response and power. Not sure if most of the difference was from replacing a cracked manifold or if it's the tubular header design over the manifold.

I used mustang exhaust manifold gasket with the mustang bolts without issue. Only thing to look out for depending on what year and what you want to do is the EGR tube and o2 sensor port.
Rangers built with Cali emissions have the EGR tube, O2 sensor port and the hot air tube so they are a direct bolt up to the mustang.
The mustang EGR valve will accept the Ranger's EGR tube, but the Ranger header will not accept the mustang EGR tube. So make sure you get the EGR tube with the header if you are going to keep your EGR functional. Other Rangers other then cali I believe did not have the EGR tube or fitting