I would leave the disc that came off it as it is. It could be that you may have to put it back on one day.
I would assume that you are setting the mower up to do mulching.
Im not sure how the 4 blade disc will work with longer 505 blades on it instead of the high lift mulching blades that the 18" mower uses.
I would be looking for a washer/spacer to use above the blade plate.
Is my math right if i say 2.2mm thick???
I think digging in the buckets of bolts etc that i have here i found a washer that was about that, i use it for putting the PT motors back together in place of the blade plade when doing the lower nut up to get the boss to grab on the flywheel.
