I need to join 420 to itself and to 316s stainless.

I've found reference in ASM Vol 1 Handbook that loosely recommends 600F would be appropriate. The only reference I find for maximum interpass is an API document that states 600F max for 410.

Would 309 filler with 600F preheat be a good starting point?

What would be recommended for maximum heat input?

Thanks,
Allen Book