Robin, congratulations on having the huevos and talent to build your own IJ molder.
Looks good. (hope mother nature feels the same way)
I think the US (mostly) uses a 0.5" radius nozzle.
It seems that a radius would make sealing better when things are a bit out of alignment or deflect due to pressures and heating.
Making a 0.5" outside radius is a bit more difficult, but the mold radius is then quite easy requiring just a 1" ball em.
Whatever you choose, good luck.