It took a little longer than I had hoped, and burned through an Intel DH61AG motherboard in the process (its rear USB 2.0 and ethernet ports died after a few days) but it is finally done and fully assembled! I decided to use the 2 LED's on the front of the TiVo for standard Power LED and Hard Drive LED. As this HTPC is a SageTV Client currently, I saw no need to make use of the Recording LED support on the motherboard. Also, all of my tuners are Silicon Dust HD Homerun products and as such I can see the activity LED's on each.
I replaced the rear TiVo fan with a Cooler Master BladeMaster 80mm PWM fan. It runs pretty slow, about 700-900 RPM but obviously can go faster if need be.
I also pulled some old power and reset switch housings from old ATX PC cases I had here at work and hot glued those buttons (swapped the actual buttons for new ones) into the two Coax input holes in the rear of the TiVo. Bottom one is power, top red one is reset. I need to pull another red button cover from an old case for the power button still.
Philips HDR212 TiVo (gutted)
Intel DH61AG motherboard
Intel G620 cpu with stock HSF and Arctic Silver 5
G.SKILL 8GB (2 x 4GB) 204-Pin SO-DIMM DDR3 1066 (PC3 8500) Model F3-8500CL7D-8GBSQ
Intel X25-M Mainstream SSDSA2MH080G2R5 2.5" 80GB SSD (re-used from laptop)
19V 7.9A 150w AC-DC Power Adapter from mini-box.com