I broke the spindle on a flat smooth road after years of casual and occasionally much harder rides. I'm not that heavy or strong, and it still kind of amazes me that it broke like that. I still wonder if it was sudden, or if I had examined it before it broke I would have been able to see anything. I think it broke right near the drive crank, outside of the groove. Sounds like it may not have been a very common problem so yours might be just fine. It was the grey/silver and blue aerospace and it had the tange chrome replacement fork on it when I got it used for whatever that's worth.
I think some have tapped it for italian, but the phil sounds better to me, maybe uses the same bearings too. I've still got that frame, nice frame, just can't justify the costs for now.
I'd try fitting a triple on the existing spindle just to get a general idea. You'll probably want a shorter one. That spindle might be a little longer on the drive side, and the tapers might even be different, affecting how far the cranks slip on, but the phil might be adjustable. Good luck.