If I remenber right,that 5s had the coil inside the flywheel ,and different style of points than the Aluminum Briggs engines had..I remember robbing a set from my 5s to get the "A" going,they were the same!..I think the "ZZ" engine used the same ones too,had a "Pincor" ? magneto..
I'm guessing that 5s is from the 40's or 50's,but I've seen a briggs catalog we had in the attic of an old parts store I worked at,dated 1935,that showed one,and it looked about the same as mine,which was a '52 model off a reel mower..I cringe now when I think of how many of those I had I didn't keep,thinking they were useless,since they only had a 1/2 crank PTO and wouldn't propel a go cart or mini bike that well,unless you geared it down enough to only go 10-15 mph!..I bet I had 20 of them given to me over the years similar to the 5s,like 6n's..
One amusement park where I used to live that went under not long ago sold off all the "midget racer" cars hey had,with old Clinton's and Briggs engines like the 5s,and I heard many sold for 1-2K!..and guys looking for engines or parts for them would pay whatever you wanted for one!..I think that is why mine sold for 75,I bet the "collector" I sold those engines too re-sold them for double that easily,if not more..
One cranberry bog my friend works at as a maintenence engineer said they had over 200 of those K91 4 hp Kohlers at one time,now they have about 75 still in use,and many of the "dead" ones stashed away for parts--but he says soon they will likely just scrap them,since the newer engines like Hondas and their clones seem to be holding up well--most of the pumps are now diesels,they used to use 250 chevy sixes,but those are getting scarce here lately too..they have tons of one and two cylinder wisconsins too,but they wont part with any of them or the parts due to rarity too,unfortunately..