You can weld mild to 304 with 316 rods but the problem is that when the mild exhaust heats up and it will a lot more with a non standard R paint even many layers of high heat stuff wont prevent it from degrading i know this first hand as i tried this before i got the goose and about a year or so and it was paper thin from about a 1.6mm wall tube. Then again i do live in the country so floods and muck on the road are common place.
But with installing the goose complete with SS bolts (can you tell i've a fetish for stainless
) ive never looked at it been on for near 3 years. So if i had of just not been so tight and bought the goose first time around i would not have wasted money on pipework.
I think i also read somewhere that the inner walls of stainless remain smooth causing less turbulance over time which is the main reason most sports exhausts are made from 304 I'll see if i can find it........... TBC ;-)