Good news and bad news for you Ace.
The PI 4.6 was put in a lot of Crown Vics and Grand Marquis. Not sure what year it started, but you can find that on Bing or whatever. They are extremely reliable and well built engines & you can find a lot of them out there.
Also note, the P71 (Police Interceptor) did not have a special engine or a special ECU. I think they are rated at 260-280hp & about as much torque. You can Bing all of this if you'd like. Having owned 2 P71s I can tell you they are not very fast cars. They have plenty of power, handle well, ride smooth and are extremely well balanced cars, but they aren't hot rods.
Between you and me, I'd wait to find a Lincoln Mark VIII for a DOHC, 32 valve, 320+hp donor engine. Its the same engine they put in the Cobra of that era & it will turn your GM into a real nice sleeper. You'll probably also want to source the tranny and find a LSD for it as well.
Good luck to you, let us know how it works out for you.
Last edited by Gator417; 07-05-2016 at 07:01 PM.