We had a 15 ft 5400 at one time.  When I switched to SI belt meters, I knew what population I would plant before I started a field, rather than afterwards.  I have seen where some people would use a length of pvc in place of some of the seed tube.  Otherwise, the seed tube would pop off of the seed boot on the row unit.  I think there were two different sizes of pvc the would slide into each other.  We carried our 5400 on an Elk Creek caddy.  It would put some negative tongue weight on the tractor when it was raised out of the ground.  It was more noticeable when the bins were full.  The 5500 factory frame had issues with the neck of the frame cracking from stress.  Many have been repaired by plating that area and still planting.  I thought I saw a different caddy on a 5500 that was for sale a year or so ago.  Don’t know if it was Yetter or someone else that made a beefier caddy.  Overall, I thought it was pretty reliable.  We worked ground before planting.