why is your cut off 1976? essentially the HS40 is 1968/1969 version1, 1970 to 1972 version2, 1973 to 1979 version3. in 1980 the crankshaft taper changes, and then things start to get weird... i would go 1968 to 1979 as the most desired years. effectively there's no difference in a 1976 or 1979 model. they both have cast iron flywheels and the squared off blower housing. What i look for is HS40 models A to F. once you hit G, you get that changed flywheel taper.
But any HS40 model A to J will have the 4 leg pull start (with J models having CDI ignition.) But when K starts to come out in 1988, the pull start changes to the Cyclone version, and i do not like the looks of those. But you can always put a 4 leg pull start blower housing on the later cyclone pull start models.
Frankly all the HS40 models are essentially the same. Sure in the 1990s they changed the piston to use the thinner rings. but other than that, they are all pretty much the same (if you don't care about flywheel tapers or points/cdi ignition or pull start variants.)
Just avoid the 1990s H40 models. those are different. essentially an H35 with subtle changes. they discontinued the HS40 mid-1990s and went to the H40, because it fit emissions standards better.