G'day folks,
I'm with CyberJack, on the head swap by a previous tenant. For whatever reason - if any...
If the barrel has the vacuum line port on the intake spigot, then it definitely had a decompressor ex-factory.
Not to detract from the performance of the machine - these were/are a great mower. My old man still has one, an ex trade-in from the 1980's. I'll check if it has the High-Comp head and muffler on it next time I visit, if I can remember to.
The only thing about this machine not having the decompressor, is that the starter will wear faster than it should - it wasn't designed for an engine with full compression starting.