I went on files.minecraftforge.net and I the minimum version that's made with minecraft forge is 1.1 release.
That's for Forge itself, not TooManyItems. FWIW, there are older versions of Forge on SourceForge, which based on the dates go back to Beta 1.7.3. However, looking at the TooManyItems thread, I only see Forge variants of the mod back to Minecraft 1.6.1.
I'm not sure what to delete in the json, but you could use MultiMC instead and install TMI as a jar mod using its interface, which I just confirmed works.
I've been using it myself for a couple of years now, so I certainly hope MultiMC is safe.
Magic Launcher that "WaltersDad" mentioned could be a decent alternative - I tried it a year or two ago, and didn't find it all that user friendly, though that might have been partly because I was trying to use Forge mods, while Magic Launcher seems like it is designed more for jar mods like Optifine or the old versions of TMI.