Having now completed the swap, here is what I needed and what happened.
1. rm250 parts purchase:
Forks, upper and lower triple tree with stem and bearings, front wheel, axle and spacers, vapor computer
2. Swap parts
The front end bolts on directly to the frame with no issues because they share the same bearings. The DR650 caliper, brake line and master cylinder can all be used with the RM250 forks.
You can use a long bolt and mount the ignition and neutral indicator to the threaded area on the front of the upper RM250 triple. Put the threaded part in between the rubber of the neutral indicator and the ignition bracket.
You will not be able to lock the steering. Get a rotor lock and a leash.
You can use pipe clamps to secure the headlight bracket to the forks on the top. This requires cutting the top of the bracket off to fit between the top and bottom clamp. For the bottom you can bend a metal bracket and use the bolts the secure the front fender to mount the bottom mount of the headlight.
You will need to tap the steering stops with normal allen head bolts to keep the forks from banging the tank.
The vapor will mount fine. I used the threaded area on the top bar clamp to mount an aluminum bracket. Or you can use the bar mount supplied.
On the speedo sensor I used the rotor bolt supplied with the magnetic part. I then bent a small aluminum strip and bolted it to the bottom of the forks where the brake line used to attach. Then the sensor attached at the other end to have the magnetic rotor bolt pass it.
I did more for making it supermoto. I lowered the forks and resprung them with racetech valves. I also laced the RM250 hub to a 17" rim.
Complete front end from a 2003 RM250: $350
Revalve and respring with lowering on forks: $450
laced rm hub to 17" wheel: $50
Vapor computer: $160
EBC 320mm brake kit: $120
( I sold the stock parts from my DR and ended up spending $450 total in the end)