I have two clutch baskets for my DT400B (both stamped 498-16311 #C-1). One has 64 teeth, the other 65 teeth. The 65 tooth won't mount with my 24T pri drive gear. In looking at Pri drive gears on Ebay, I noticed 23T units for the DT250B. I'm assuming that the 64T driven gear matched with the 24T primary drive gear is the correct pair for the DT400B, and the 65T basket/ 23T drive gear are correct for the DT250B. Can I run the 65T/23T set on my DT400B? Does it make a difference in pull resistance or clutch wear?

You would be changing the primary gear ratio so yes there would be a difference in "pull" and the perceived "gap" between the gears. 

It's not much of a change so I doubt a "butt dyno" would know the difference. 

Can't see clutch wear being affected. 

Beside the part number there are some kind of hand-engraved numbers on both wheels. I have read somewhere, Yamaha did it in the factory to dedicate matching gear wheels for each engine case. Don't know if it's true,  but most likely,  yes. If wear of the basket is the reason you want to switch, I would keep the original drive wheel pairs and just rivet the better Aluminium basket onto your clutch drive wheel. To all the experts in this forum,  please correct me,  if I am wrong. 

Thanks for Info. I did notice the etched numbers on each, but don't know how to reference them. I'll look into swapping baskets, but I'll stick with the original drive/driven gears for now.