The original manuals don't come cheap - I paid over $30 for mine, but it's in almost new condition.
You said you are missing the front needle plate - this is what is on the missing one. I've seen plenty of earlier Davis machines without that, but they also take the longer needle.
Here are a few pages from the manual to get you started (I don't know how to use the scanner - and DH is not home right now).
And yes, it has the flat needle bar -
this might be better
it has reverse! (I see yours has this lever too) Interestingly, this picture shows a different tension dial than the others in the manual.
Of course, I had to get one because of the neat attachments it take
