MKIV GSR with Type E MkV. The date of the filter, September 1939, is interesting as I didn't think they were making MkV filters this early. Some info in comments. : r/gasmasks
PS-1004 K&N Pro Series Oil Filter for Mitsubishi Cordia GSR AA, AB, AC Turbo 2.0 | eBay
Amazon.com: DNA High Performance Air Filter for Suzuki GSR 600 (06-11) PN:P-S6S06-01 : Automotive
British Army GSR Respirator & Filters Military Gas Mask - Size 3 [JH07 – Pools Surplus Stores