Check with Joe, he may know if any of the builders have openings to get your amp done. I think me and Lee figured out that Parts alone were nearing $1000. Labor would be about 40-50 hours worth. I usually don't recommend pumping that much into a 400 when the parts are about the same for a 700B/II
You could easily have $1800 into a 400 and a 700B (if you have a core) would be not much more. It all comes down to selling in MY book. WOPL'd 400's don't go for nearly as much as a WOPL'd 700B/II and you'll get twice the power (500WPC RMS out of the 700). They are not cheap but for an amp that will last you a lifetime????