Thanks for all the fast responses.

I can still find some 11-28t 8 speed cassettes around. Many are "-I" cassettes, e.g., HG70-I. My understanding is that these are not road bike compatible, correct?

There are some others such as the CS-HG51 (Alivio) 11-28t 8 speed cassette that are not "-I" models. If I got one of these, would my RD be adjustable to accommodate the 11t gear?