There's an old-school trick of stripping #12 Romex and using lengths of the bare copper wire on the PCB traces and soldered (usually done with a gun before adding any components), Not recommended for mass-market manufacture, but for a one-off? Works great.
Another old engineering trick is to never exceed 70% of any device's capacity. If you want to have 70A of current, then use devices with 100A rating. Given that your devices are rated 50A, limit your design to 35A.
A trick I saw Vari-Lites use was Boost Converters to get voltages up to +500VDC for routing around in the chassis (these were for the motor drive circuits). That way they could use smaller wires at lower currents. Then, when they needed the high currents to drive the motors, they would Buck Convert back to lower voltage. They used Boost and Buck converters with DC like transformers work for AC.