Which deck do you have? The LX255 is pretty old (20 years?) and I think it could be had w/ 3 decks. The 42C deck was, in my opinion, problematic with 'blow out' under and out the sides as I recall - it generated too much lift and didn't route air flow well.

Yup, 42c
I had them put an anti blow kit along the the front lip that cured the blowout problem. The mower decks on the newer models have optional mulch plates that block off discharge when you need it. I wonder how an add on plate would work

Can't help you specifically. I bought a 44M for my 255 and fabricated a plate out of tin that will last a couple few seasons but I'm comparing apples to oranges.

My 42C doesn't have that kit (does it help?) but I stopped using it except to move leaves from along the fence - got tired of the dust storm in kicks up in my sand conditions! It dispels with such force that over the years it has sand blasted holes in spots on the deck thru ablasion.

If you can't find a blocking kit - you might fabricate a temporary one as an experiment out of thin metal like tin. If it works get or more permanent one made up. Sorry can't help more this.

(off topic by the 42C has only 3 wheels - sometimes it scalps a little).

They also made a deck called the 'Freedom' deck for those tractors as I recall - had no discharge at all on either side.

Thanks for your input on the subject. Happy mowing!