The step itself is as listed on the Catalina Direct web site, but I think you've probably seen this in their on line catalogue-
I bolted that to the hinged stainless part with countersunk bolts from the bottom. (That's Ballinger Spars part # B HMB M30-I don't have an image of that part.)
The holes in the aluminum step from Catalina Direct didn't match up with the holes in the stainless hinged step, so I redrilled the holes in the aluminum step, and then had a local stainless steel fabricator fashion the rectangular stainless backing plate placed on top of the aluminum step.
I think I used black electricians tape, (or maybe Tek-Gel, the memory's a bit foggy on this), between the aluminum and stainless to reduce dissimilar metals corrosion.
And I sunk the assembly into thickened epoxy in the cabin top, as suggested in this web site:
Judy B's "Bijou" - A Catalina 27 Website
It's done now, but if I were to do it again, I would seriously consider somehow through bolting the assembly to the cabin top-the way I did it, you have to be super careful not to put too much upwards pressure on the step assembly when preparing to step the mast:
Resting the mast on the stern pulpit with the base attached to the hinged assembly on the cabin top puts a lot of the mast mass behind the stern pulpit, pulling upwards on the step with a lot of leverage, and may pull the whole assembly out of the cabin top. (We had a poor shlep sitting on the pulpit with the mast on his shoulder as I did the final preparing of the shrouds, and this lessened the leverage, so all went well. But I had to rush it for the sake of his back and shoulder...)
Not to go on & on with this, but as it is installed at present, I think when I unstep the mast next time I'll make the 2 X 4 A-frame I've seen suggested on You Tube, with the top at spreader level, and ease the mast down with a line running through the top of the A-frame. Then the line over the top of the A-frame will support much of the weight of the mast when it's down, and I'll be able to detach the base of the mast at the hinge and ease the base forward.