Literally pinned 2 threads above yours. https://www.corral.net/threads/anything-everything-gt40p.1014187/

 

Figure out your header/spark plug situation while they are off the car.

 

This spark plug socket from Trick Flow usually solves the problem with spark plug access...
Used this socket on my " P " heads with two different sets of headers...
I recommend this to all who have headers.......

 

So what I discovered with these heads is that the exhaust ports are offset below the centerline drawn between the exhaust header mounting holes. Pretty much any header will fit, but depending on the size of the exhaust port opening in the exhaust flange, you may or may not find some exhaust port alignment concerns. As mentioned above, that thread has quite a few links to threads that discuss the header options and would be worth reading to determine what makes sense for you based on what is currently available today.

The GT40P heads are quite an optimized casting, so aside from upgrading the spring pack, there's not a lot left to do. Porting can result in a ruined head pretty easily because the castings don't leave a lot of material for much work, but a little clean up doesn't hurt. These heads came stock on my '00 Mountaineer and it definitely wasn't slow.

 

What???
The difference is the sparkplug angle/location.

 

What???
The difference is the sparkplug angle/location.

There is a port offset issue as well compared to all aftermarket heads which have their exhaust ports centered between the bolt holes, generally, unless they use the unique patterns for some of the Trick Flow heads and others.

 

Theres a reason p heads are dirt cheap... They are not worth the hassle.

 

Here is a better link to that socket..

Trick Flow® Spark Plug Sockets TFS-90500

www.trickflow.com

 

P heads on a truck aren’t really an issue because the service manual even says to access everything from within the fenderwell

 

I ran P heads with long tubes 20+ years ago. On the drivers side I used Accel "shorty" spark plugs (don't remember the number) for header tube clearance and for plug wire boots at the plugs I used small 90* distributor boots and terminals. Had a spark plug socket with the side cut out that I could slide onto the plugs sideways. Only massaging was to remove the thermactor bump in the exhaust port but have to be careful because P heads have a water jacket around the exhaust valve. Just get rid of the bump. Don't enlarge the ports just clean up any casting ridges on the exhaust and intake. I polished the exhaust ports. Clean up the valve bowls. If the stock rotators are still on the exhaust valves, get rid of them. I also added high temperature valve seals. I found that the motor didn't need as much initial ignition advance due to the centrally located spark plug. My motor like 8* initial advance.