I would just like to confirm for all of you questions, I have an original CECHA 60GB Fat PS3. I used to run Hermesv4b PAYLOAD with 3.50 Spoof via 5g ipod/Rockbox. This version is also a 256MB NAND version.
I updated from OFW 3.41 => OFW 3.55 via USB Drive, and in the XMB. I then HAD TO boot into Recovery Mode. Once in recovery Mode, I installed KMEAW CFW 3.55. After this I installed 3.55 Multiman, and then LV2.pkg.
I restarted my PS3 then, and ran the LV2 patcher, and pressed X (quits back to XMB).
I was then able to Launch Multiman (latest version, signed for 3.55) My old versions of Comgenies File Manager, OBM, Gaia, Cracked PSN Games (for 3.41) no longer would launch, so I simply deleted them. Any 3.55 package I install from this point should work.
I successfully Launched GT5 (after changing my modded EBOOT.bin from the 3.41 compatible one back to the original one compiled for 3.50+) I successfully Launched several other games, both diskless and with a disk in.
Call of Duty: Black Ops would not launch. There is a simple reason for this though. I have modified files I had after backing it up to make it compatible with 3.41 When I get home from work today I plan on deleting it, and backing it up, then it should run like normal.
Also GT5 updated to the latest patch, installed, and ran afterwards. I was also able to connect to PSN while in GT5 and talk to my friends.
One thing it seems everyone is doing is trying to boot from Multiman directly. When it asks you to boot without exiting to the XMB, say NO. Mount the Disk to PS3_Home/DiskImage just like you used to with OBM and Gaia back in the day, and launch it yourself from the XMB.
It should all work perfectly, I've tested it on my own console, its an old model with 256MB NAND (CECHA-FAT60GB). I have not tested blu-ray movies on it afterwards however. That is the only thing I have left to do.