How to get size of a 3d object from a viewport and convert to UDim2

[NinjoOnline]

I want to make this purple frame (2d) match the same size as the blue part (part inside a WorldModel inside a Viewport) and make its size match

coroutine.wrap(function()
	while not Done do
		local vector, onScreen = Camera:WorldToViewportPoint(WorldModel.BottomHalf.Position)
		local screenPoint = Vector2.new(vector.X, vector.Y)
	
		script.Parent.Card.Position = UDim2.fromScale(vector.X, vector.Y)
		
		task.wait()
	end
end)()

I got position working, so the frame follows and matches the correct position of the blue part, but I cannot figure out the math for making the size match the blue part