I think it's a High Standard. Here is a Model 28 .pdf schematic.
http://pdf.textfiles.com/manuals/FIR...higgins_28.pdf
"Sears model 583.71"
The Blue Book lists the 583.7 as a High Standard Model 10.
I haven't found a Model 10 rifle yet, but the one in the .pdf file looks a lot like the Flite-King pumps.