That plate looks like the one that I have on the '84 LT4000. Plow number is 486.244072. It's a 42 inch, single spring. The push beam is abut 4 inches wide and has a rod perpendicular to the push beam that fits into the notched hole, held in by a small 'l' shaped fitting and a snap pin. The push beam extends back mid way and ataches to the raise/lower mechanism that used for the mower deck.
Take a look in the sears website and put in that number. A parts diagram should pop up.
The push beam shouldn't be that hard to fabricate once you get all the measurements.