what rate is your new spring? once done with this latest round of mods you'll be moving faster and still need some shock adjustment to avoid that interference issue. you need to free up that rear brake line in the guide.
the HEL lines are a good idea, but if you didn't order a HEL front line sized for the DRZ400, you'll find the Versys spec line too short for your new big boy DRZ forks. the stock DRZ banjo ends will work fine with your setup.
the adapter to mate the Versys/ER6 caliper to the DL1000 wheel/DRZ fork setup looks like this
several clearance issues, so you'll end up with a complex shape. these adapters are commonly fabricated in aluminum alloy, but i chose steel for this critical part. i suggest you check the ER6 forums and research the common 4 pot calipers that are swapped onto the ER6 bikes. the OEM Versys caliper provides very good braking with a 310mm rotor, but since you haven't fabbed an adapter yet, now would be the time to go 4 pot. the caliper is cheap on the used part market, and the adapter would look very similar.
front axle and spacers are easy.
you're going to wonder why you didn't mount those 49mm forks sooner.