I need scope bases for my long action Steven 200 in .270. The end of the receiver is round. I have no idea whats good or bad I'm looking at either a Vortex 6x40 or Weaver K4. Do I need extended bases... One piece or Two piece?!

Can you guys just give me links to something that will work... Im so confused as to whats good or what will even work. I want it mounted as low as possible. Well... Within reason. Bolt needs to be able to cycle.