Hello,
What do you mean by base model? R5k? I did a complete write up (see below link) to upgrade a R5k model to R10k/R12k.... for some reason I can't get the images back up, I'll try and fix this tomorrow. (EDIT - Photos restored!) You should not have to hack away if you already have the chassis version with the removable drive bay plate.
http://forums.irixnet.org/thread-578-pos...ml#pid4352.
There is also a wiki article here
https://wiki.irixnet.org/Upgrade-SGI-O2-...-to-10-12k
SSD - Yes you can, but you are going to spend A LOT of money on ACARD SCSI to SATA adapter...if you can even find one. They sell for around $1,000 on ebay now. Your best bet is install a quiet 10k / 15k SCA SCSI drive. The 10K 'newer' 10K versions produce less heat.
The skins are a easy straight swap...However the 'old' style skins are quite hard to come by so I'd hang on to those. In fact, ANY good O2 skins are hard to come by.
You will also need a R10K/R12k PCI riser, R10K/R12k motherboard tray.