I've made mine pretty much the same shape and size as the genuine 50s versions below (I based my measurements on a pattern for a 32-34" bust, and seeing as I have 33" bust the sizing is pretty spot on). I added a wider cowl neck to made it a bit more modern, and I think the dolman shape needs something up top to make it look balanced. I've kept the 3/4 length sleeves, but I think it would also look good if you continued the ribbed cuff down to the wrist. My cuffs are actually 4" but folded back.
The sleeve seams were a fun challenge. I didn't want a sewn top seam as I thought it would be too bulky in double knit, and I wanted it as invisible as possible. Kitchener stitch was the obvious solution, but as the sleeves are a triangular shape the top of them needs to be progressively shaped. I improvised a method involving putting stitches on spare needles, but it was clumsy, and I have little uneven bits where I turned the rows. In hindsight I think I could have used short rows to shape the top of the sleeves - next time! The end result is pretty good all the same, you can just see the seam on my left arm, It's less visible now after a wash and block.
This is my inspiration in it's purest form - Stitchcraft 1950. Do you see what I mean about this shape needing some balance? I find that really tight neckline unflattering (not to mention uncomfortable).
The obligatory dolman sweater pose! This one is interesting because they've got around the top of the arm seam problem by adding in a crochet panel. Needle and Thread magazine, also around 1950.
The pose again - I'm going to have to get another pic of mine in the correct pose! This one is from a Modella booklet, I'm going to have to guess 1950 because 1950 seems to have been the year of the dolman. For a brief time the knitting booklets and magazines were full of dolman cardigans and sweaters, several in any given issue. The shape shows up again around 1960, and in a wider "batwing" form in the 70s and again in the early 80s, but never seems to stay in fashion for long. So I figured I'd better knit mine quickly before I tired of the style ;-)