I made one of these for Cutty1 here on the sight and I was lucky to get two 3-1/8" gauges and three 2-1/6" gauges in.
You might be able to do the 3-3/8" and two 2-5/8".
Now of course this all assumes you do it the way I've done it here. But if you build a panel that comes out more flush with the dash surround, you'll gain more clearance. It just depends on how "factory" you want it to look. I was going for a well integrated panel that didn't look like I bolted something in for a race car but rather something the factory may have done.
If your going for more of the race car look then doing a larger alumiunum panel might work for you.
Here's the gauge panel I made for Cutty1. You can see how tight things were: