Electrode 308 and 316 Material

You'll need a lawyer for this one, and an engineer. One of those high priced MIT engineers.

What does the spec say?

Unless this is an exhaust header on an Indy car or a Porsche headed to Sebring, you would be hard pressed to notice a difference and, even then it would just be a different colar after the race. It would be helpful if the use of the weldment were included even is it is only a comparable/similar setting.

the main difference between 308 and 316 stainless steel is that 316 contain 2.5% molybdenum , 308 ha no molybdenum . basicaly 316 used for high temperature services and presence of molybdenum in 316 provides creep resistance at elevated temperature and pitting resistence in halide atmosphere .

In term of technical respect machinibility , weldability and strength wise there are no big real difference between 316 and 308.

If I called myself "vessel guy," I would be using a qualified Weld Procedure Specification (WPS). The WPS will list the base metals and the filler metals that can be used while welding. The base and filler metals are essential variables that cannot be changed without requaliying the weld procedure.

I think you're OK, as I recall you can use any combination 300 series austenetics for base and filler. Someone (like vessel guy) with access to ASME Sect IX can look it up.