Nice piston BB have seen a few like that myself,a little harder to get out.
In regards to the head without the decompression valve not a common head but not rare either. They did come out in the early to mid 90's.Usually on the boring base models the ones that were cheaper.I'd say it was due to cost cutting being cheap and saving on the decompression valve.
The cowls you were talking about were not what was mentioned but in fact from different time periods.The first one with the power-torque on the plastic came from the late 80's to early 90's,and the one you have put on was later and they still can be purchased now.
Your first engine could well have been the earlier powertorque and may have had more cooling fins on the engine block which would fit the time period for your first cowl.
Hope that doesn't sound to confusing.
