1984-1988 small frame H and HS shrouds are direct fit for your late model engines, you will want to source the flywheel screen as well as your late model engines did not get them. 1974-(1972 for HS50)-1983 are close but come into contact with the external coil your engine runs...they can be squeezed on with some rigging, not something I would personally do, I have used a 1981-1983 specific flywheel and Points ignition system when I have had to build a specific engine for someone that needed that era/type shroud in the past though.
The chrome shroud on the right is an example for the 84-88 version compared to a 74-83 version shroud on the left in white, note they took the top of the shroud out flush with recoil bumpout for airspace/clearance when they went to external mounted electronic ignitions.
The only way to backdate your engines to the early rounded thin shrouding would be to swap out the crankshafts to earlier pre 1981 versions so you could utilize the 1968-1974 HS40 only thin aluminum flywheels, your era engine has a 10 degree tapered shaft where the earlier engines have a 16 degree taper. the thin HS40 are the only FW's to clear that style shrouding and work with your engines (also note that HS40 and HS50 crankshaft ARE different, so you need to make sure you are using the correct shaft for whatever engine you build if you take it that far) as well as all the other parts and pieces (shroud, backing plate, cup/screen, Flywheel nut/belleville washer, magneto, etc..) confused yet
