The first block of numbers would be prefixed MODEL: so your engine is most likely a 131922. Its type is 0138, and its trim is 01. The code tells us it was manufactured on 10 August 1982. Hence it probably has Magnatron electronic ignition (1982 was the changeover year). Here is the illustrated parts list:

http://bsintek.basco.com/BriggsDocumentDisplay/Z6mltJVJ1DajI.pdf

Here is the operator's manual:

http://bsintek.basco.com/BriggsDocumentDisplay/msotJO-K_ny7tH217FzoPu.pdf

The engine is 13 cubic inches displacement (210 cc), of the second design generation, with a vertical crankshaft, Pulsa-Jet carburetor, a ball-race upper main bearing, and a rewind starter. (An electric starter was optional, but your engine does not have one or the model number would end in 4 instead of 2.) These 5 hp engines had an internal centrifugal governor in the crankcase, instead of the air vane governors used on the smaller Briggs engines. I rely on Joe's evaluation of the engine: I haven't used or worked on one of this model.

I suggest you make a careful inspection of the gearbox to see if you can find a manufacturer or model number (preferably both). Also, the gear ratio layout would help the ride-on fraternity here to identify it. I'm guessing it is a three speed plus reverse type, but which gear is where, and does it have an X pattern or an H pattern?

It looks prettier than a Massey 35 to me, in fact prettier than a Massey 42. I don't really see all that much resemblance to any Massey. The closest I could come on the spur of the moment is the IH 585, from 1981-1985 (which by a strange coincidence lines up fairly well with the engine's manufacture date). Great looking machine, though. What does it use for a clutch? From the layout in the pictures it looks like the clutch pedal moves an idler to tighten the engine-to-gearbox V belt.