I thought the ethernet chip is supported in plan9 so that might be easy. vl can generate elf files, these are targeted at sgi machines but most of the groundwork should be there for you.
Failing this I am pretty sure I have a motorola S record generator somwhere, I will convert the input side to plan9 a.out if I can find it. IMHO v[cla] is the way to go. -Steve