Your answer makes no sense. Are you familar with AWS welding specifications, and welding Ni-containing steels? The SA 537 Class 1 steel is a C-Mn-Si pressure vessel steel plate, that I doubt will have suitable notch toughness at -75 deg F. You will probably need a Ni-containing steel to weld to SA 203.
Get your hands on one and look for FCAW weld electrodes (SFA 5.29). In this specification, there are various weld electrodes with Ni contents that provide impact values of 20 ft-lbs at -75 deg F. One is E8XT5-NI2C. Check with Kobelco Welding, and deal with their technical support not salesmen.
The E80T5-Ni3 will make your properties at that CVN temperature. Last time I checked, ESAB didn't make that wire. ESAB does make an E80T5-Ni2, but even though ESAB does make some very good wires, their basic slag wires I have used leave some room for improvement. (More spattery smokey compared to some other basic slag wires). The only manfucaturers I have found that make E80T5-Ni3 is Select-Arc in Ohio, and Devasco in Houston. None of the Ni3 wires tend to run very smoothly, and you will probably get some complaints from your welders. It is just a hard composition & properties to make and have a smooth running wire.
A wire I have used before that does run much better than the Ni3 wires that might make your -75F is the Select-Arc 812-K2. I qualified a WPS on A352 LC1 with it.
