Lawnboy sold separate adapters for the different models that would convert to bagging, mulching or side discharge. On my model, the mulching apapter is just a plastic plate that bolts on in place of the bagger chute. You might want to google lawnboy parts to see if you can source it.

You can generally find the various plates on ebay. Ideally you would have a 'blank' plate for side discharge and a 'block-off' plate for mulching to go with your bagging chute. Frequently the discharge plates are black, but that's no problem. The various plates and chutes are all interchangeable on staggered-wheel housings.