To answer the OP's question, I'm going with "Yes". You're ss derailer will work finewith your ?x28 freewheel, when coupled with your 52/42 crankset.
To bring the discussion to a more interesting area: what DOES determine the maximum size cog an RD can handle? The cage's length has more to do with chainwrap capacity, of course. And, most of shimano's current road derailers list a 28t max cog, whether we're looking at ss or sgs versions. (Which backs up Hillrider's comment). However, I have a short-cage 105 rd from ca.1990 that was doing duty with a 14x34 6speed freewheel when i got it, so...? Also, many recent short-cage mtb rear derailers from shimano and sram can rock 34t cogs, but can't handle excess wrap...
So, what does determine the max cog size?