You can keep your subframe. S52 is more documented and easier than s54. Do some reading on 24v swap section (all the stickies at least) on r3vlimited.com and/or e30tech. Again, there's LOADS documented on the m/s5x swap that can give you a complete parts list and much more.
If you're looking for s54, keep in mind theres also other swaps that can do the same power cheaper. +1 on stance factory they do a ton of theses was very well.