How can i fit a clutch to Briggs and straton 5.5HP Vanguard?

I have acquired a b&s HP vanguard ohv engine (type 007801 md115432 code 94022849) that was attached to a generator and i would like to fit this to a go kart for my lad. the end of the crank is tapered and dose not have a key and key way. all the videos and info ive got shows the clutch located buy a key and key way. should I change the crank? and if so can any one help find the correct part number? im a bit stumped.
many thanks