As mulching kits for both J-N and RM series mower decks are scarce, there is an option that I came across that may be of interest. Recently I had a 1987 448 with an N46 mower deck here that belongs to member 24mee for major repair work on both the tractor and mower deck. When I got into the mower deck, I noticed a modification that I hadn't seen before and wasn't sure how it affected the mowing quality of the deck. I had to replace the spindle housings/bearings, spindles and all pulleys. All the time doing this I was concerned about the metal bars that had been welded in between each blade area. I also replaced the center drive spindle pulley with one for a J-N40 which increases the blade tip speed significantly all the time wondering how the deck would perform. With the tractor running, the deck installed and adjusted, I mowed part of my lawn and I was impressed with the cut. Usually with the height of grass that I was mowing, the grass clippings would have accumulated into noticeable rows but this didn't happen. The deck was discharging a smaller amount of clippings and they were small. So I concluded that this deck with the separation bars was partially mulching and partially discharging. The tractor went back to the owner who was very pleased with the mowing quality of this deck.
This is the only pic that I have of the underside of this deck and the metal bars that had been welded in are 1 1/4" to 1 1/2" wide. P7280002.jpeg
When the leaves get pretty thick on the lawn and I would have to keep emptying my bags I just let them get full and let the chute get plugged, I just leave it that way and finish cutting the grass and it does a pretty good job of mulching them and then I just go back and go over the lawn cutting again and have less times emptying the bags..