For OEM bushes I've seen people put a large jubilee clip round the outside edge, compress them, position them in the bush, then release the jubilee clip - allegedly works well. Use a quality jubilee clip though, not Halfrauds cheap tat.
Also, you need to bolt it all back together in roughly the standard static position of the trailing arm - this is the preload element, as they don't rotate freely like the Powerflex ones. The preloading can be tricky, but just try to gauge the angle of the trailing arm to the housing as best you can, and tighten it up as such.
The E46 M3 bushes are supposed to be good (yes, they fit, and they're the same as the E36 M3 ones (all E36 & E46 RTAB's are interchangeable). I have powerflex ones though. As said above, I wouldn't use them for FCAB's (lolliopos in the front) again, but they're good as RTAB's (very good indeed) and easy to fit.
HTH