Carb - BST28 sounds right, but I really don't know.
Airbox is the same, but the duct is different.
Horsepower - feels like 18; just a guess.
CDI is interchangeable. People say the DR250's spark advance is more aggressive, and they are probably right; I've found if you put it on a DR350 with a higher compresison ratio (10.5:1) it will ping below 7000 ft elevation.
I never noted what my stock gearing was on the 250. Something to keep in mind is the 250 has a different primary drive ratio than the 350, so you really can't compare final drive ratios with the 350. Most of the time I run 14/47 on my bike which has the 250 primary drive and tranny.