here is something I found on a hs-50 points head. note on the head where the holes are. the casting for most of the holes have a wide area. this was something not found on the early hs-40's
I do recall talking to a retired engineer from Tecumseh last year and asking about the hs-50 motor and telling me they new right away that there was going to be a 5hp built shortly after the 4hp. but first they had to do some retooling. I think this head would make sense why they would do something like these. nothing to do with heat.
if you look at the head you can tell it has two parts to it. upper and lower. making it more cost efficient to drill out bolt patterns for small bore engine by using one upper casting. for example a h30 motor . lower casting may have been replace when casting for a small bore ,so the cc's would still come out correct.
so many little changes Tecumseh did in the early days. I do personally like the early hs-40 with the small bolt pattern. that can be a plus when hot rodding and you bore it .010 , .020 or better yet using a wiseco .080 piston. the first design head and gasket set is small keeping the cc's up when boring the motor out. newer hs-40's with the larger bolt pattern you need to watch for the correct head gasket. you could lower the compression with a hs-50 gasket.