Sizing Rectifiers

Sorry, this is a little off-topic--but the group has so much
horsepower.

Suppose one is making a power supply to deliver 250 amps at 30 volts
DC 60% duty cycle from three phase 230 using 3 single phase matched
transformers and a full wave bridge consisting of 6 diodes. The
ultimate load is resistive (arc welding). What amperage rating should
the diodes have? Even at full output each diode doesn't feel the
entire current all the time--right?

I have checked some authoritative sources, e.g. Motorola Rectifier
Applications Handbook, but wasn't entirely sure of what I was reading.

Maybe every shop electrician knows a rule of thumb that covers this
situation?

Thanks in advance.

-Jack