The Dunlop K180 is a street legal tyre suitable for dirt track. These tyre are cheap enough
you might as well give dirt track/speedway riding a try and see if you like it.
On the front use a K180 or a soft terrain knobby like the MX33. The DT3 is a race only dirt track tyre that is not street legal. These are medium compound versions. For a 250 4 stroke use the 130, 450 4 strokes use the 140.