Power lift question

I am trying to estimate how much weight a power lifter could draw on a footbow. I know an average man can draw over 300 lb. When the bow is shot the shooter is laying on his back with his legs in the air braced against the bow so the arrow will be released at about 45°. So he is basically holding the string with his hands and pushing with his legs. I am thinking about a thousand pounds would be doable but would just like some other opinions. His hands are not directly on the screen he is holding a bar with a release mechanism attached to it.

That motion sounds similar to a deadlift, and the record for deadlift is around 1,100 pounds.