I took one of these 67mm pistons and sent it to Venolia and asked if they could make me a 70mm one.
They said for $200 no problem.
It uses standard Yamaha 70mm rings and a standard Yamaha 16mm wrist pin. The rings are the same width, thickness, as the TW rings.
I talked to a lady at Venolia and she said if I wanted another piston just to give them the work order number and they could make one. Possibly if you are interested you could give them the number but stipulate you want a 74mm piston. The other thing is the rings -- if the thickness of Yamaha 74mm rings is the same as that of the TW you would be in business.
But be aware this will NOT be a drop in piston. All volumes will have to be measured and the dome will have to be reduced to lower the compression ratio. And the valve to piston clearance will have to be checked. BTW, the dome is solid and very thick. Plenty of metal to work with.
If you say to Venolia "I want a piston of 11:1 compression the will work with a TTR225 crankshaft in a TW 200 engine case" they will say back to you "send us the dimensions you want and we will make it for you."
Now if I could only find the work order number....................