On the one spindle type swing I made I did not weld the spindle in at all. I used 2" X 4" rect tube and using a hole saw I drilled holes in the bumper. I then cut a piece of some 1 3/4" OD by 1 1/4" ID DOM tubing to fit in the bumper. I welded the DOM into the bumper. The spindle fits into the dom and is held in by 2 3/8" set screws. I'd think you could do something similar.
2006 Solar Yellow Rubicon Unlimited
Jeep Club Member #1340
6 Speed, Hardtop
Mods done: Hurst tee handle, cheap hand throttle, Rokmen Merc front bumper, Warn 9.5 TI winch with 3/8" X 100 worth of Viking yellow rope, DPG OME Ultimate with JKS ACOS up front, Kilby Gas Tank Skid, Kilby Steering Box Skid, Jeep Medic Belly Up, Skidrow Engine Skid, Rockcrusher Diff Skid in the rear, Warn Diff cover in front, , AR Outlaw II's and MTR 12:50/15's, Homemade rear Bumper, Cheap Cobra CB, Puma OBA, Sirius Radio, Locker Defeat, Rockhard cage, Rockmen short corners, homemade tire swing/tailgate hinge affair, Airlift air bags on the rear- - - - - - and more to come!