Our 420 came with a drawbar towball which works well with a Thule Xpress 2 bike carrier which we already had. I have found however that with our bikes (full size 26" trail bikes) they did get in the way of the jockey wheel adjustments so have just modified the carrier so I can put one bike on each side. This is simply putting a new hole through the center of the carrier bars and moving the bolts /brackets to the middle.

With the handlebars swiveled round and the inside pedal taken off they are a pretty good fit allowing full adjustment of the jockey wheel. You cannot open the gas locker whilst this is fitted but then we couldn't with the original configuration either.

20190108_121829.jpg - Bild entfernt (keine Rechte)

20190108_121414.jpg - Bild entfernt (keine Rechte)

20190108_121428.jpg - Bild entfernt (keine Rechte)

Like that!
Will be doing that soon.

Seems to work ok. You could consider offsetting the new hole to give more clearance at the rear. It depends very much on the bike. These are quite old now and newer ones seem to be more compact but didn't want to buy new bikes .