There is no doubt your panel will fit in the plane. That being said, you are kind of pushing the limits of height that I normally like to see in the side by side RV's. Literally every side/side panel we do is extended somewhat, but I like to try and keep it within 1-1.25" of Van's original panel. Several good options have been mentioned, like the relocation of the EIS, possibly using 2.25" backups, etc..
Overall, it really is like Matt said. It depends on what fits you. Me, that would be too deep, even with my preference for cut down sticks. For some, it's fine and no problem. I know you're a bit more constrained than we are with not being able to relocate/modify the braces on the panel, and a slider would give you a lot more wiggle room for location of 'stuff', but you are where you are and I think overall you'll be ok.
Moving to a smaller GPS would and smaller backups would give you back a lot of vertical space. For example, a Garmin GPSxxx would probably allow you to put the EIS over in that stack if you want, and with the smaller backups it'd be easy.
Now for some separate critique (actually just my opinion). I try really hard to keep things as symmetrical as possible in a panel. For example, I'd like to see your screens on the same horizontal plane. That means moving the compass so the screens can be aligned. Using the new ProPilot from Trio or a Digiflight II from TruTrak will save a lot of space being used by the AP section. Actually, I'd shoot for the Digiflight IIVSGV, because it couples nicely with the GRT's and is only 2.25" in diameter, or 1.25" tall in a flat version. That frees up a ton of room. You've also got a lot of freedom with the AOA display (it can be moved up and over) as well as possibly using the PM3000 vertically to get that room to use. In all reality, with a little tweaking you should be able to have a "double width" radio stacks between the hinges, allowing you to keep the AvMap if you desire, but in order to do that you'd need to downsize to the 2.25" backups, get the TruTrak AP, and a few other tweaks. Then you'd get back at least and inch or so on the bottom of the panel, and the other plus is it would get back to being a bit more symmetrical as well as giving you a bit more freedom on locating things more traditionally. It'd also allow you to get the switches back on the pilot side of the aircraft....or were you planning on flying it from the right seat? If that's the case, then perhaps relocation of the Autopilot, et.al makes sense as well. I have a lot of ideas, but not enough time to type them all out. I like to make things ergonomic and usefull, as well as being pleasing to the eye....makes flying so much more enjoyable when everything is in easy reach as well as looks good!
Anyway, I could ramble on for a long time, but if you're interested I think you could easily get things lined up nicely and still fit everything in a neater package as far as height goes....just takes a little tweaking. Contact me off list if you'd like some free advice. I'm happy to do a quick/sloppy layout for you for free if you can handle it taking a bit.
My 2 cents as usual!
Cheers,
Stein