If you were to adjust the tension, would it solve your problems? Are you just using it for straight lines, or are you trying to perform miracles? From the picture you posted, it looks very clean to me. I'm sure you did what you could to gussie it up prior to sewing. As far as the vintage, my guess is mid' 60's. That was sort of a pre-cam era. The later 60's is when boxes of cams were part of the package, and in the mid to late 70's is when cams were a thing of the past.