I just picked one up, too. 3312grs, s/n B380101388. In a package deal. Real 'quiet' engine. Uses absolutely no gas. Pushes easily. Nice big hole behind the starter, in the engine. Bummer. Previous owner ran it without oil. Missing the engine compartment side panels, but no rust anywhere. Has the mower deck but missing the raise/lower contraption for it.
The 3312 is similiar to the Bolens 'Suburnan" ST-120, except for the color, Red vs. white & green.
The rear has the tiller attachment arms, and it has the 'tiller' transmission, whatever that is.
Supposedly made by MTD Products.
Parts manuals/lists are on the web. Operating manuals I have not been able to locate. Have not seen many parts for them on eBay.
I'm looking for a replacement 10 - 12 hp. vertical shaft engine to get mine going. Until then, it just sits.