I just put a Rockware D-90 bumper on my series 3. Just bolted it right on. Bumpers that use the sleeve under the frame horns won't work unless you do a little welding. Do a search under Rockware and you will found where I aske dthe same question and people posted pics.
'73 SeriesIII coiler,"The Goat", Daihatsu 2.8TD,Santana,Ashcroft,ARB's,etc., now SOLD