OK, I'll try to close this thread out a bit for anyone interested. I started it with a question about spreaders. For the record, and my boat is a '78, hull 148, the correct spreader is an SP 512 (as Ed has stated) mine has the twist lock end, fits over a spreader base with a hole for a clevis pin through the spreader and the base, and mounts to a 7747 mast. I tried ordering these from Rig Rite who sent me very specific information in the only email I got from them on what they had in their warehouse, only to find out they didn't have it all after numerous follow up calls. They stated that they are making changes in their equipment and will be able to turn these out with a 6-8 week lead time. Unfortunately, other than having a shop tool up to produce these, they may be the only option for replacements. I gave up and had mine welded and saved $1000 and 6-8 weeks of the sailing season.
As far as my mast step is concerned, Rig Rite had it from mid December 2012 and finally shipped it to me last week, late March. No reason to order these from anyone other than Carter Fabricators, already mentioned on this thread. I have never worked so hard to spend $1500 on my boat. A learning experience.