I learned on an early 90's yamaha 280 4 stroke. A few years later i bought an atk 250cc 2t that didnt have a power valve. Now I have a 01 rm250 2t that i am re-working for more power.
If you can excersize a bit of throttle control and not be wfo out of the gate, I think you would be fine since you have a little street bike experience.
Edit: Dont we have a proper forum for this shit?
"I've got a message in a bottle, written in gas and oil, signed with a rag and a match"