I just did this and it's pretty straight forward, get the right size coupler for your tongue tube size. I used the weld in one $65. (the bolt on's about $20 more) If I remember right you can go out to 4' but the weight rating decreases. There's a chart in the instructions to figure your final rating by the length after coupler.
With tongue supported by a floor jack I moved the trailer jack back to where it needed to go, then used a
metal chop saw held in place by the clamp on the table and a floor jack and wood block to cut it.
For cheaper options to cut it I'd recommend an angle grinder with a cutoff wheel or a last resort a sawsall. The chop saw or angle grinder give a more easily controlled cut to keep things square.
With the swing coupler (both halves bolted and pinned together) in place I clamped a straight edge to the side of the tongue on both sides of the coupler to help hold it straight/inline side to side then leveled the tongue using the trailer jack and used the floor jack to level out the other half to match.
There was some eyeballing until I was happy that it all lined up and welded it in place. Being an amateur welder I enlisted the help of my uncle who's a pro welder so that I would trust it. LOL
For bolt on I'd use the same process up to the welding but drill and bolt the three open sides one bolt at a time (one side covered by the clamped straight edge) eyeballing my alignment for the first few. Pull the straight edge off and finish the last side of bolts. re run your trailer wire harness and you're done.
You will also need longer safety chains as their attachment point needs to be moved back to behind the swing coupler and you'll need to ad some sort of keeper hoop up by the ball coupler to keep them from dragging.
