You've just described typical "alpine gearing" of bikes from that era. You can use any Shimano small cage derailleur that will handle a 28t low. Light Action offered a top model in the 525. But sounds like you don't care to repeat the spring mishap. I recommend one of my favorites, the 105 1050 series. From the same period, an upper level offering.
Others are Exage 400 or 500 EX short cage models. A little later, an RX100 or RSX short cage (these are basically OEM models of the 105). Higher still, 600 SIS.

A long cage will require extra chain links, which I assume you still have for the KMC.
If you decide to pick up a long cage....
Exage 400LX, 500LX, Altus C10, Alivio, RX100 long cage, Deore, or Deore DX.