Well... we all learn from our mistakes! After painstakingly taking my Mac Pro 2006 apart, installing the 2nd hand x5355 chips - I got it running like a champ! Checked it out, 8 cores, started right up whooo hooo! ehh then I quickly realized the CPU fans weren't running. No problem I thought, they must not be properly connected. I opened her up, re-seated the fans and the... ehhh, yikes, no power! No click, no LED on the front panel, nada, zip!! After exhaustively looking for what could be wrong, sigh!, nothing. I reset the SMC and when I when I push the diagnostic button only the trickle power supply lights up.
Sooooo I might just have a 50 lb paperweight on my hands. Live and learn.
I ordered up a used APPLE MAC PRO (EARLY 2008) 2X QUAD CORE 2.8GHZ 4GB 320GB 8800GT 512MB-VRAM LOADED for $1K that'll be here in a couple of days. I'll strip the whatever I can from my old mac and maybe re-sell it for parts or just donate it. I might take it to a local shop and see if anyone can revive it or search for a cheap cheap used power supply just to try it.
In summary, I'm pretty tech saavy, I was very careful in the procedure, it worked for a while, I just got unlucky. If you attempt this yourself, I'd pause to consider the possible risks. Also while I love the design of the Mac Pro overall, some parts are difficult to access and put back. Probably the worst is the front fan assembly.