If it is a true HS40 one, its part number 610845. They were used on the earlier electric start HS40's and they had an odd shroud that was sort of a cross between an early round top but were widened at the bottom like the 1972-up HS50 and post '74 small frame H and HS engines got. Becuase of that most, if not all of them got a little tag like the 1972-73 HS50s received which was attached to the small bolt that held the deflector shroud on above the PTO snce standard tags of the time would not fit. The baffle was wider and configured like the later models I believe as well.
Here is a shot of the funky shroud: