If you're planning to replace the trailing arm bushings, the springs have to be removed. When the springs are out is the perfect time to do subframe bushings. I did everything (and I do mean EVERYTHING-shocks, springs & pads, axles, diff seals, diff mount, trailing arm bushings, subframe bushings, sway bar end links) on the rear of my 300D at once, and without the springs putting tension on the subframe the subframe bushing bolts just slide right in.

By the way, a $40 Harbor Freight ball joint press is the perfect tool for pressing trailing arm bushings in and out. You just have to cut the rubber lip off the old bushing to give the press a place to seat and they pop right out. A little brake grease on the new bushing helps it slide in easily without tearing the rubber.

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1982 300D, black w/ palomino leather, 203K
2001 E320, champagne, 105K (Mom's)
1999 Dodge Dakota, squeaky & battered, 142K