I'm not sure the exact size of the wastegate. What I did was; I took out the 2 bolts that hold the end of the turbine housing (plus the 3 from the exhaust pipe of course) and that exposes the wastegate. With it closed I sprayed it with ink (or paint whatever you have on hand) then remove the wastegate and finish disassembly of the turbine housing.

I then took a die grinder with a rotary file bit and carefully removed metal until there was 1/16" of metal until the paint line evenly all the way around. That is the new remaining seat. I then opened up the inside of the wastegate port to provide a large smooth flared entrance into the port. I switched from the rotary file to a flapper type of sanding wheel on the die grinder to polish it smooth for flow. That probably wasn't necessary. I've had no issues with boost creep.

It took probably a little more than an hour of work.

I read somewhere that you can replace that little flapper disk on the wastegate with a larger one, then you can really hog out that hole, but I haven't found that necessary.

Todd