Roller cam thrust

Can someone educate me on what I need to do for cam thrust when switching from a flat tappet to a hyd roller cam? My understanding is that the lobes on the flat cam are tapered to make the lifters rotate. This forces the cam to the rear of the motor against the plate. However, a roller cam has flat lobes so there's nothing to keep the cam from moving forward. Correct? So there's some type of thrust bearing or cam button that I'll need? Does this ride against the timing cover? Will a double roller chain and a thrust bearing fit under the stock timing cover?

What's a good combination of adjustable roller sprockets and thrust bearing that will fit under the cover?

I've seen the billet AL covers that Mancini sells but is that necessary or does it make things any easier?