Chef -
Welcome to the enabler's club .......... errr .... I mean, welcome to GJ.
Looking at the parts diagram from Sears, it looks like you may have found a previously unknown grinder of the type that we call a "
pre-block". Your description that the "rear has no
"lip" for adding lamp fixture" got me thinking.
My 1/4hp pre-block has the
115 prefix (Packard Electric) in the model number, yours has the
397 prefix (Paramount/Allegretti) that the later Block Grinders had (along with the
257 prefix). I wonder if yours was built after the vendor change, but before the design change from pre-block to block. These could be the transition years.
As for the date, the pre-blocks had a date code on the data plate like the motors of that time. You can see on your label a code of
E-62 (or 61?) under the AMPS. That would mean that your grinder was made in 1962 (or 1961. It's hard to read under the paint in the picture).
What is the wheel diameter ? Is it a 6" wheel ?
Tourqeman may want as much info on your grinder as possible, so that he can add it to his database.
Thanks, I captured the label and added it to my 'library' of pictures.
Now, that database you speak of is a project I'm hoping someone will take on. I don't really have one for Blocks other than the ones that have passed through my hands or that have yet to escape. 
Plus - WE NEED MORE PICTURES !!!!!!
EDIT -
I found it in the 1962 Sears catalog on page 968. (clipping included)
Please let us [at least me!] know where it is, I haven't found the 1962 one.