If you wish to get your inventory back rename level.dat_mcr to level.dat in your game save directory.
Also look in your resource folder (and the one within DIM-1) and remove the .mca files which are the anvil ones. Minecraft 1.1 uses the .mcr while Minecraft 1.25 uses the .mca and will convert the .mcr files to .mca if it needs to.
The only thing I have lost now are the achievements and the mini map waypoints.
Any idea where these are stored. There might be a backup in the .technicssp/backups folder that I can restore.