I just finished mounting shifts on some ON3P's that had STH1's. I haven't heard any reports back on this, so thought I'd throw this out here.
For the toe you can reuse the rearward holes from the STH's for the 2 middle holes for the shifts. They seem to be a perfect match.
For the heel, the most rearward holes conflict. Since the heal on the shift had 30mm, I just moved the template about 16mm forward.
Top is towards the tip of the ski, dots are over the old STH mounting holes, X's are shift mounting holes, Circle w/ X are the shared toe holes.
Attachment 401343
I used the template for the toe as it's printed at my 326 BSL, but moved the heel template forward about 16mm, so I'm putting the 309 mark on the line to get this offset. You can see where I punched out at 340 to move them back for my first attempt, but didn't like where the heel ended up in the track.
Attachment 401344
This is how the heel piece ended up, not much room for a bigger boot, by my feet at this point aren't getting any bigger, and I just got new boots. I'd rather have more brake/heel on the track than less.
Attachment 401345
SoVT thanks for your response before, I was attempting to respond using my phone and ended up deleting my original post. I considered what you said, but ended up with Shifts. We'll see how it goes. I have some friends on them and they're not having any issues. I'll report back.
Also thanks to Lucknau and I think Knut for the template. It's perfect. I went with 65,5 mm from toe hole to center holes. I have no idea why Salomon didn't make the large cutout a little smaller and the slot a little longer, but I agree it really seems 66ish is where it should land.