Hope this helps. I have a 4HP Snapper with Wisconsin-Robin. I've had this mower for 13 years now and it ALWAYS starts in <3 pulls. ** Read: Extremely dependable engine. ***
It's now just Robin and they're owned by Fuji Heavy Industries (Isuzu, Subaru, Robin, etc.)
From a domestic standpoint though, GMC owns 20% of Subaru and has very strong ties with Isuzu (new Duramax diesel).
If you decide to buy the engine and need parts, there's an industrial supplier here in Tulsa who can get parts for my mower, so they should be able to help you should the need arise.
My two cents: Since owning the Snapper, I've researched and become a Subaru owner too. As far as trucks: Chevy, GMC...
I'm a firm believer in these engines.
BTW, Snapper still installs Robin powerplants on their 21" walks.