What was surprising on the journey was the preamp audio coupling caps did not need an upgrade. Never experienced that. The only other upgrade I'll try in the future is the phono RIAA section. Simple to build a small module. This Fisher has a rebuilt PS and uses a choke. Possible no one had tried that.
Love my 400. Took a break from my Heathkit W-5's today and put it back into the main rig. There is certainly a sweetness that only those Fisher's can bring to the table. I like mine nekkid however.