I'm not sure but I think you will run into problems around the bell housing area if you are using gt40-p heads, I believe the p heads have higher ports. There are discussions on here about it.
I had P heads on mine years ago. No difference in port height. Had to do some grinding on the flanges of my Hooker 6901's to clear spark plugs and used "shorty' spark plugs on the driver's side because the plugs are directly underneath the header tubes on that side. Also used short terminals and boots like used on later distributor posts for plug terminals.
What process on putting the 6901 Hookers on? Does engine need to be out or will they slide in from the bottom? Starter need to be off?
Easiest way I've found is to put a board and jack under the engine oil pan and unbolt the motor mounts. Raise the engine up a few inches so you can move it side to side. Move it to the passenger side first so there is room on the driver's side to clear the steering box. Install the header from underneath. When that's bolted up move the engine to the driver's side and install the passsenger side header from underneath. Some say the passenger side header can be installeed from above on their cars. Lower the engine and bolt to the motor mounts. IIRC the starter can be in place.
If Here's Jeg's link for installation https://www.jegs.com/InstallationInstructions/500/520/520-6901.pdf From my experience installing them in my 71 Grabber the instructions are pretty accurate. If you have a column shift, you'll need to remove the linkage, it will be in the way. You also will need to get a drop down bracket. It will have to be trimmed to clear the header on the side. https://www.jegs.com/i/Patriot+Exha...nj8MeqcqsAlKxaGTVaItMXdbYDswADXRoCc60QAvD_BwE It's a tight fit, but they will go. Took me about 5 hours to put them in. Start from the back when you put the header bolts in.
You'll need to put the engine on a hoist. I'd leave the trany hooked up while you lift it. Here's the installation instructions from Hooker. There are specifics for the Maverick listed in them. These worked pretty well for me when I put them in my 71 Grabber. If you have column steering, you'll need to remove the linkage and go to a floor shift. There's not enough room. Also, if you have power steering, I've added a link for the drop down bracket you'll need to clear the headers. you'll have to grind of the back edge so it clears the header and mounts to the frame. It took me about 5 hours to put them in (with help). They will only go in from the bottom. Do the driver's side first (Per the instructions). I lost my religion multiple times while putting them in, but the end result has been awesome! I also suggest getting insulation blankets to install around the collector to keep the head off the starter on the passenger and brake lines on the drivers sides. It is a tight fit, but they will fit. I've attached pictures of my install to hopefully help. https://www.jegs.com/InstallationInstructions/500/520/520-6901.pdf https://www.jegs.com/i/Patriot+Exha..._QuT9aAsCYaL8YD_veJF3dSt5o7cd0SBoC0wMQAvD_BwE