Your post caught my attention, because of Seattle, WA. are you sure he died l949? Did he have a younger son named after him? Did that Sydney Allen, Jr. and his wife adopt a son David Allen? I am the love child of this David Allen, never met the man. Born in 1955, Kathleen Marie born to Jacquilene Hill, very small cute little red head gal. This David Allen's father's name was Sydney Allen. I met a Mr. & Mrs. Sydney Allen unknowingly as a very small child in 1960's? Seattle, WA. no contact after that, my mother was very wounded from the experience, and being a single mom in1955 was not an easy thing. However, I did have 5 aunts!! and believe me, I was spoiled beyond belief. I could try to get more information from my mom...she's 73 and her memory comes and goes.
I will await your advise, and hopefully get more info. from my Mother.
Mrs.Kathleen Cook mother of 3 daughters, and one sweet grandson born just this last Valentines Day, now how sweet is that!