What is the most effective way to replicate Motor6D.Transform?

Something like this in the video below?

BTW I think what you are doing is overwriting the .Transform animations, maybe consider *= to add in animations perhaps.

	local stepped = rs.Stepped:Connect(function()
		if plrNeck then
			plrNeck.Transform = plrNeck.Transform * neckTransformOffset
		end

You can even experiment with swapping the order, just a tip or thing you can do if you find something off with your CFrame.

	local stepped = rs.Stepped:Connect(function()
		if plrNeck then
			plrNeck.Transform =  neckTransformOffset*plrNeck.Transform
		end