Jeff,

Look hard before you start cutting to move your springs inboard of the
frame.

My first thought was the same when installing my Quick Change rear end
into my Conestoga.  After looking at the spring angle, the frame angle,
change the spring angle (?)...etc., etc.,.  I figured I'd be adding
about 100lbs. "more", to the back of the car to make leaf spring
brackets strong enough, reinforce the frame enough, to hold everything
up...properly.

Four link....na, don't want to cut huge holes in the floor.
Four bar....na, want some adjustability.
Ladder bar...na, see above. Even bought these....but after holding them
in place under the car....wasn't happy.

Ended up using early (late 60's to early 70's) Chevy truck arms with
coil-overs.  Ride is great, bolted coil-overs to the axle, have
adjustability (in front bracket), rear sway bar bolts to the truck
arms. Wish bone keeps everything centered. Everythings tucked up nice
and snug about even with the frame bottom. "Not" counting the rear end,
the weight "addition" wasn't worth worring about, less than 30lbs.
Now, the rear end weight difference....!

Very happy with the setup.