Every job is different. Here is the company that makes couplings that work great for such projects. Use a Fernco coupling at the cast iron pipe and then replace all the rest with PVC.
https://www.fernco.com/plumbing/flexible-couplings/stock-couplings
That link has everything except the one he needs.
http://www.homedepot.com/p/2-in-Ser...h-40-PVC-Compression-Donut-P22U-205/100372278
Check that fitting, it may be just screwed into the cast. It might be hard to get out out but easy to replace.
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