What i would like to do is to install the Sun Blade 150's CPU into a Sun Blade 100. The 150 has the UltraSparc IIi, 550 or 650 MHz and 512 kB of L3 cache. The 100 has the UltraSparc IIe, 500 Mhz and 256 kB of L3 cache. I did not know that there are two types of UltraSparc IIi and the later one is also called IIe+; all the manuals mentioned it as UltraSparc IIi.
So if i can install the IIi (IIe+) into the Blade 100, it will run on 500 MHz, a decreased clock rate, which means less heat will dissipate. The power supplies are identical, 1.7V and 3.3V.
The Sun Blade 100 and 150 are almost identical, the only differences i found are the cooling (which is irrelevant as the CPU will run on a lower clock rate), the power consumption (i can install a bigger power supply if needed) and the "CPU grounding ring" which i did not have time yet to check what it is.
The manuals says, it cannot be upgraded, but did not elaborate why. Maybe it's just not supported, but not impossible.