The open-source FEA software called "Z88" uses kinda 20 types of elements (2D and 3D). You can download the manual and read more about these elements, maybe you will find the answer of your question there.
This is the direct link to the manual...
For such a thick foundation I usually use 3D elements (solids). In your case it would be 3 layers x 0.40 m or 4 layers x 0.30 m. The XY size of the solids would be adequate (0.30`0.50 m)
In such a situation I would use "Sika Latex" or something similar to provide the adhesion between the "old" and the "new" concrete. Together with dowels of course.
I would try to do something like the sketched in the attachment. Would pour additional concrete around and under the free edges of the footing so that the part that's over the elevator pit could be neglected (demolished). The change of the shape in plan is a try to avoid or minimize the change...
Holo-bolt or self-drilling screw would do the job. The second one is most common in my country. The other option is to design produce something that looks like the part that I showed you and weld it to the steel part.