Identify Briggs engine fitted to Norlett rotovator?

I have a Norlett rotovator fitted with a 3 hp horizontal shaft Briggs Stratton engine. However the original model and type number has been lost due to a replacement fan cowl.The engine has 4 tapped holes on the side cover around the output shaft. Possibly this is to mount a reduction gearbox?
The Norlett uses it to mount the vee belt clutch arrangement.
Can any one suggest engine model and type numbers?

Ken Cocks
May 2010