although everyone says you need the blobs saved, i personally downloaded 4.0 for 2g mc model and restored it through itunes and got zero errors.
It was restored from 4.0.2 to 4.0 and also the jailbreakme website told me that it would be impossible to restore it back
Maybe i added an address in the hosts file which skipped the blob check but i am definitely sure u can do it without shsh. Alidsl has definitely more experience than me so maybe there is a catch
I did not use blobs... just changed an address in the hosts file and used the 4.0 firmware to restore