Two things to think about...
- the top bolts on a stock crossmember to frame are a pain to remove and replace, drilling new holes up there is not easy.
- accessing the rearward pan bolts on the 700r4 is very difficult if not impossible on stock crossmembers.
For $40 or so a CPP tubular crossmember is a good deal if the above are important to you. It bolts on the bottom flange of the frame only and allows access to pan bolts.