do the newer hs40s have a cast iron flywheel like the hs50 ?
yes, even the small frame H went to Steel wheels and removable fins during the 1974/75 time period. That's when you see them convert the numbering system and throttles as well. The smaller HP (3.5-down) engines were the last to get the flywheel and shroud update so you will find them in later '74 with no riveted on ID plate and number stamped on the top like a later square shroud engine has
There was just a discussion on here about the aluminum flywheel that was on the early/first HS50's, I am not sure when they changed but I would bet close to when they were deciding to convert the 40's over to the same style shroud. so if you have an HS50 that is not stamped on the top of the shroud but has kind of a dogtag bolted to the output side there is a good change its going to have that early aluminum wheel on it...I dont know if that's good or bad, you would not have to worry about glue failure on the magnets since they are cast into the AL but the steel wheel is probably stronger and the fins are replaceable.