whoa there - I got thrown by the throuds and was still thinking about Sealandroader stays so my post probably don't make a lot of sense - yep might have a long search looking for a die that size.
Agree with the use of an old sealholder.
And on the subject of such, I've just had mine off the Flash, it can be a bit of a struggle, I found a good tool is one of those rubber straps that you wind around and through the handle which has teeth that grips the belt, normally pretty useless I've found BUT think maybe I was using it wrong, wrapping the belt around the threaded bit of the seal holder merely tightens the threaded bit to the thread on the fork, if you grip the very top of the seal holder it seems to get a better grip and puts no pressure on the threads - result mine came off no problem and had been on for around thirteen years at least