i do remember someone had posted about putting one of those rear bumpers on (recently). They didn't go into spesifics but they noted that they never wanted to do it again, it took them about 3.5 hrs., bolt holes didn't mesh well, and they needed 2 sets of hands.
If it came to the point of having to drop the tank and removing rusty hardware. I would deffinatley get all the parts that you might need to replace before hand, esp if its your daily driver.
but i would wait for some more replys to see if there is anymore ideas out there, i have yet to replace my stocky with anything else.