You might post a WTB thread in FS/Trade for a couple Alpha P3125's, or as I mentioned before, the Globalwin VOS32. The "rear" CPU would need a P3125 that's been shortened up, since there is typically not enough room between the two CPUs for an unmodified P3125.
Even with these top-notch heatsinks, the CPUs will run very, very hot without forced-air cooling. I still think you'd be best off using just one CPU for the purpose you stated previously.