My advice: Shorten up the head, use a more robust sinktip.
For 60-70ft casts you can go to a Rio Windcutter, Airflo Delta, or SA short head (cut) (54ft heads, 6ft leader, shoot 10ft of running line - pc of cake) with a 15ft type 8 tip and that will cast and bring the fly deeper. Or with the Rio Windcutter you can upsize the line to a higher line weight and remove the center section, creating a shorter "Skagit" style setup, using a section of T14 which is serious sinktip, and that should get you there.
Reason: the more compact the grains and diameter of the line pushing the tip, the heavier the tip can be.
If you need to go more than that you need to find different water to swing
note: if you are standing next to the chuck and duckers and indie boys you might not be in good swingwater anyway. You want to be able to cover water where the fly can be slowed by tension through the swing to pass in front of the fish where they are holding, including the hang down. In many spots where weight and indicators are effective the fish are 90 degrees to you in other words the path of the fly / hook is upriver and straight across in front of you instead of swung down and across with a nice s-l-o-w pass. If depth is so important, than the spot might not be the best as steelhead will move for a fly in the right circumstances and these are the ones where the swing is king. Find a stretch that you can cover with successive swings where you can apply tension on the line, slowing the fly through a slow swing, and hanging down in a likely spot for a grab as well. Then step through the whole run, systematically covering every fishy inch. I have found most indie / chuck and duckers to stay put in one spot, which is another thing that works against the swinger whose game is coverage.