Arrange the 4*2 like this

Top down view 2 inch side showing so 4 inch is the height.
Then put the plywood on the top and screw it to each 4*2 with maybe 3 screws per wood.
To add to the stability cover the ends too with plywood and screw with 2 screws per wood.
If you do that and use 3/4" plywood it will hold the TV no problem, like I said it will take my weight, AND WAAAAY MORE.
3 lenghts of 4*2 is is enough BTW, I just draw 4.