Talley makes extended front bases. You should get an additional 3/8 inch of movement. I've learned this before and always buy the extended because it gives you more options.
The one screw should be shorted to fit in that forward screw position otherwise it may bottom out on the barrel thread before it tightens. Don't screw down the rings til they touch - you wil crunch the tube body. Buy an inch/pound wrench - it is your friend.
Keep us posted as to how it all works out.
