What is the minimum acceptable intercooler piping size for a 617?

The biggest diameter I can use in my plans is 51mmOD because of clearance issues. I have access to lots of Saab 900 piping that would fit my needs very well. But, it's cast tubing instead of regular rolled tube. That reduces the ID to around 45mm. Would that be okay or should I look for some traditional 51" aluminized steel tubes?

It will be used with my VNT turbo running about 1bar of pressure.