Engine runs fine but seems to seize after wot

...or by saying it seizes, do you mean it starts to crank and it stalls your starter due to too much initial timing?

After following the suggestions above and IF you find the motor turns over manually and is actually free to rotate, I would suspect if you retarded your initial timing you will eliminate the hot start problem. OR

You can also try to crank it with the ignition key in the off position, go under the hood and jumper the starter relay to see if it will spin over when there is no power to the ignition. If it spins with no ignition on, you may have a bad ground or too much initial advance.

Once in a while when my car is hot on a hot day, I have a switch to kill the ignition power until I get the engine spinning with the starter, then I flip on the power to the ignition and it fires right up. I have 12.8 to 1 compression, and my initial timing is set at about 22 degrees before TDC. This happens occasionally even with a strong mini starter and a big Oddessy capable of a 5000 amp dead-short with 0 gauge wire going directly to it and a 2 gauge ground cable going directly back to the battery. Plus my block is grounded to the car, as is the battery.