You mean as far as mounting or wiring it in? I'm assuming that you could wire in just about any gauge. Unless the SPT gauge has a special harness or something, even then if you know the wiring diagram you could probably do it. Can I ask why you want the bar gauge? If you are just getting it b/c it's SPT, I might reccomend going with something aftermarket. I would think it'd be hard to prove that a boost gauge did damage(unless you do a really bad install?). I have a Prosport 52mm mechanical boost gauge and I love it. I hope I helped, if you have more questions let me know I'd be happy to help.
Yes, I have. I took the Lamco gauge out of an 04 STI. I chose it because it did the job I wanted while looking like the car shipped with. Doing the bar conversion wasn't an issue for me. I knew the boost my car should make in bar, so no big deal.
Anyway, I tapped the hose that comes off of the BPV with a plastic tee I bought at home depot, then my friend and I spent 2 1/2 hours finding a way to route the vacuum line, and then another 20 routing the vacuum line through a tiny opening in the glove box, behind the dash and to the steering column where we mounted the gauge. We almost had to take apart my entire interior. Glove box door off, radio out, dash panels unsnapped, and steering column cover off. We got it all back together ok, though. No extra mystery screws.
There's no grommet in the driver's side floorboard that we could see. If it was there it's buried under 4 in of sound insulation. lol.
I then had a tech at subaru of gwinnett tap one of my radio illumination wires to light the gauge up when I have my headlamps on. Cost me 30 bucks in labor, but I'm electrical illiterate, so I paid for it.
Good luck. It was PITA. If I knew it would be such a hassle I would've waited to buy some Defi's. An electronic gauge that reads off of the ECU would probably be an easier install, even if it's a tad more expensive.