Repair frame

[Jonesy]

gday gary here, this is the chassis one on my early 70 model G60 Datsun ute, its the only rust in the chassis and inside of chassis has been inspected with a plumbers flexy long camera, this truck has never seen the beach as its always lives in the WA Wheat Farming Region, there was a lot of dirt and shit build up behind steering box, How can I fix this chassis properly, thanks