It has taken a little while to work this one out – methodically going through RCAF aircraft made in USA with small engines.

The original premise that this was the top deck of a single engined aircraft was shown to be flawed by the lack of dzus fasteners.

I am now 95% confident in assigning this as the upper port oil tank cover of an RCAF Beech 18 Expeditor.

The comparison with the Dutch machine ( and others ) shows the correct shape; rivet count and spacing around the edges.

The early P&W engined machines had a US 8.5 gallon oil tank which is close to the 6.6 imperial gallon markings.

https://www.ipms.nl/walkarounds/walkaround-vliegtuigen-props/465-walkaround-beech18.html#

I attach pics of the panel and the close up of the same panel in situ from the IPMS link.

Only leaves the Canadian foundry piece to be assigned