Upgrade JB 3GS to 3.1.2

[jminore14]

My 3gs is jailbroken on the factory installed 3.0.1

I just never got around to updating it... Now I'd like to do a restore, and now I'd like an updated firmware, but having heard lots of horror stories about 3.1.3 I figured I'd go with the 3.1.2

I tried this and got the "the ___ iphone could not be restored. This device isn't eligible for the requested build 3.1.2"
After some extensive googling I found out something about Apple not signing SHSHs anymore or something like that. I'll be honest, I don't really understand all that much about it.

Can anyone tell me if there's a way to not have Apple sign whatever? I read something about doing an offline restore so Apple didn't get to see it, or somehow faking itunes out so it thought that Apple saw it, or something like that. If it's not possible with 3.1.2, I'd at least like something a little newer (I'd like MMS). I plan on re-jailbreaking after my restore, preferably using blackra1n. If there's any additional info you need to assist, please let me know and I'll post it.

Any thoughts? Thanks!

 

[Applejuiced]

Open up Cydia and look at the top of the page if it displays something like this:
This Device has SHSHs on file for iphone OS: 3.1.2
if you do have cydia installed and clicked "make my life easier" at one point back then you can restore to the firmware listed there. If not you will not be able to restore to anything but the latest 3.1.3 and in process losing your JB and unlock.