If I am not mistaken the main difference in the accessories and pulleys is the mustang setup sits out much farther, therefore causing clearance issues with the fan and radiator. An electric fan setup may correct that issue for you. I have a 91 5.0 that I may look into changing to the mustang setup when I get my engine built. That's mostly due to wanting a custom setup and that is something you will not find for an MN12 chassis.
I'll second the cam, heads and intake idea. While I've had fun with my 5.0, it's not quick. 3.73 gears made it much better, but still not worth the swap in stock form. Headers are also an issue, but you can read up on that in the forums- lots of discussion and good info there.
One cheaper idea for heads and intake would be Explorer heads (GT40) and a cobra intake. You can find those pretty cheap. Decent cam, springs and timing chain, and you are close to 300HP with supporting throttle body and MAF.
Last edited by Zep5.0; Today at 04:58 PM.