You can certainly attempt it if you like, it's always interesting to see a new project come alive.
Firstly, most importantly:
The Radeon/FireGL keeps itself cool
so long as the thermal paste is working. This is the most important thing to cool since it's stuck to the board and you can't easily replace it.
Next, the CPU:
My experience with T500 with ATI Radeon 3650, and W500 with the OnFireGL, is that they perform exactly the same.
I managed T500, R500, R61, T61, T60, R60, Z61, X61, X60, Z60 etc.. with all manner of CPU and GPU, including the 25W P-series CPUs (including the 27W P9700) and the 35W T-series CPUs and the 35W Celerons.
My experience says all the Core and Core 2 CPUs irregardless of wattage rating, Ghz, and core count perform with the exact same perceived speed of
SLOW. However, they do get the job done. The only meaningful difference is that the lower wattage (25W, 27W, whateverW) P-series run a good amount cooler than the 35W T-series and 35W Celerons.
So I would suggest, before going through the effort of dumping ice buckets on these computers, just install any P-series CPU and go about your day.
Here is a list of the processors:
Core 2 Duo P7350 SLB44 (C0) SLB53 (M0) 2 2 GHz 3 MB 1066 MT/s 7.5× 1.00–1.250 V 25 W Socket P Mid 2008 AW80576GH0413M AW80577SH0413M OEM
Core 2 Duo P7350 SLG8E (C0) SLGE3 (R0) 2 2 GHz 3 MB 1066 MT/s 7.5× 1.00–1.250 V 25 W FC-BGA478 Mid 2008 OEM
Core 2 Duo P7370 SLG8X (R0) SLGF9 (R0) 2 2 GHz 3 MB 1066 MT/s 7.5× 1.00–1.250 V 25 W Socket P January 2009 AW80577SH0413M AW80577SH0413ML OEM
Core 2 Duo P7450 SLB45 (C0) SLGF7 (R0) SLB54 (M0) SLB56 (M0) 2 2.13 GHz 3 MB 1066 MT/s 8× 1.00–1.250 V 25 W Socket P January 2009 AW80577SH0463M AW80576GH0463M (C0) OEM
Core 2 Duo P7450 SLGFF (C0) 2 2.13 GHz 3 MB 1066 MT/s 8× 1.00–1.250 V 25 W FC-BGA478 January 2009 AW80577P7450M (C0) OEM
Core 2 Duo P7550 SLGF8 (R0) 2 2.27 GHz 3 MB 1066 MT/s 8.5× 1.00–1.250 V 25 W Socket P June 2009 AW80577SH0513MA OEM
Core 2 Duo P7570 SLGLW (R0) 2 2.27 GHz 3 MB 1066 MT/s 8.5× 1.00–1.250 V 25 W Socket P Q3 2009 AW80577SH0513ML OEM
Core 2 Duo P8400 SLB3R (M0) SLB3Q (M0) SLB52 (M0) SLG8Z (M0) SLGCC (R0) SLGCQ (R0) SLGCF (R0) SLGFC (R0) SLGCL (R0) 2 2.27 GHz 3 MB 1066 MT/s 8.5× 1.00–1.250 V 25 W Socket P June 13, 2008[36] AW80577SH0513M AW80577SH0513MN BX80577P8400 $209
Core 2 Duo P8400 SLB4M (M0) 2 2.27 GHz 3 MB 1066 MT/s 8.5× 1.00–1.250 V 25 W FC-BGA478 June 2008 AV80577SH0513M $209
Core 2 Duo P8600 SLB3S (M0) SLGA4 (M0) SLGFD (R0) 2 2.4 GHz 3 MB 1066 MT/s 9× 1.00–1.250 V 25 W Socket P June 2008[37] AW80577SH0563M BX80577P8600 $241
Core 2 Duo P8600 SLB4N (M0) SLGDZ (R0) 2 2.4 GHz 3 MB 1066 MT/s 9× 1.00–1.250 V 25 W FC-BGA478 June 2008 AV80577SH0563M $241
Core 2 Duo P8700 SLGFE (R0) 2 2.53 GHz 3 MB 1066 MT/s 9.5× 1.00–1.250 V 25 W Socket P December 2008 AW80577SH0613MG BX80577P8700 $241
Core 2 Duo P8700 SLGFG (R0) 2 2.53 GHz 3 MB 1066 MT/s 9.5× 1.00–1.250 V 25 W FC-BGA478 December 2008 AV80577SH0613MG $241
Core 2 Duo P8800 SLGLR (R0) 2 2.67 GHz 3 MB 1066 MT/s 10× 1.00–1.250 V 25 W Socket P Q2 2009 AW80577SH0673MG BX80577P8800 $241
Core 2 Duo P8800 SLGLA (E0) 2 2.67 GHz 3 MB 1066 MT/s 10× 1.00–1.250 V 25 W FC-BGA478 Q2 2009 AV80577SH0673MG $241
Core 2 Duo P9500 SLB4E (C0) SLGE8 (E0) 2 2.53 GHz 6 MB 1066 MT/s 9.5× 1.05–1.162 V 25 W Socket P July 2008 AW80576SH0616M AV80576SH0616M $348
Core 2 Duo P9600 SLGE6 (E0) 2 2.67 GHz 6 MB 1066 MT/s 10× 1.05–1.212 V 25 W Socket P December 2008 AW80576SH0676MG $348
Core 2 Duo P9700 SLGQS (E0) 2 2.8 GHz 6 MB 1066 MT/s 10.5× 1.012–1.175 V 28 W Socket P June 2009 AW80576SH0726MG $348