No free information that I know of
B & S put out a 300 odd page manual to cover the stuff they have no intention of digitising called
"Service Manual for Out of Production Engines 1919-1981" part No CE8096-5/00
You will probably find a copy in a real library and definately in a trade school library
As for IPL's very little chance of one of those anywhere apart from an old time mower shop ( not many of them around ) or on one of the forums dedicated to old mowers like VintageMowers.net but that is a pay ( $ 5 ) type forum that seem to scare most away .
Now for your parts book
The important bit is the first 6 numbers 092908
All of these engines are basically the same and the search results for 092908 yielded 89 pages of results .
The next bit 1204 is not all that important as it describes the trim colours, decals and perhaps the fuel tank
But in your case 1204-99 is there , both an IPL & owners manual
The 01 usually means no special branding so the engine would just have B & S decals and no mention of MW.
Now as 092908 codes out as vertical shaft engine with Pulse jet carb & side pull starter
Google B & S engine codes .
So that is most likely to be a Side Valve ( flat head ) engine and that engine ran on till the 2000's by which time a SV engine could not meet emission standards so it should also be covered by a latter publication
"single cylinder L-Head air cooled engines
Note both of these manuals cover a multitude of models so you have to do some selective reading to extract the information you need
