Engine runs fine but seems to seize after wot

So I have checked everything I can think of except the trans. It all idles fine, has good fuel and oil press and timing is good. Coolant is also good. Shifts fine and can drive around but the second you accelerate bar or go wot the engine seems to seize. The same happens when it's in park in the driveway at wot. Won't restart after this. Let it sit for 3 hrs or so and it starts up as before. Any help would be awesome. I have been trying to do some research on line and on this site as well. The car is a 72 duster with 70 340 and a 904