I have the exact same year Def 90 (1994) and also had a rotted rear cross member. I had a post not too long ago (week or so) about my rear member replacement. I had a shop do it and I went with the RN galvanized version that included extensions and rear spring mounts. I can say that I am extremely pleased with the fit so far. I don't have the vehicle back yet as I have some other work being done.
I also had the shop send the galvanized rear member to be painted. It is a little more work/labor to do so with prep involved but since I wasn't doing a complete frame replacement I wanted it to blend.
When all is done its getting a treatment of Waxoyl to further blend the old and new. Also like you my rear step bumper and rest of my frame was in great shape. I just had them hit the rear step with the same black paint to blend it all.
Doing it yourself will save a ton of cash. I wish I could have. I'm about $9k into the repairs (including parts) already but that is not just the rear member/extensions I had other things done including the rear tub tube that is just forward of the rear wheel well. Mine was rotting at the ends where it bolts to the body.
You may want to check your tub tube if you haven't already.
Link to my original post on this: