I wonder if these might work??
http://www.gas-n.com/home.html
I have run them on both my 347 and 392 and can say that nothing else I've tried (stock FFR and lobaks) comes
even close to the quality appearance and sound!! If you give Georgie a call, perhaps he can provide the answer. My thought would be that he only need change the header to pipe flanging to open up his product to a world of SPFs ...or alternately that they may already be a fit if you run his stainless headers.