How can i convert Block/Item IDs in a world?

[Dylan Madigan]

I have a little modpack for myself and my friends. We're finally rebuilding it from 1.4.7 to 1.12.2. 

We don't want to lose all the buildings and skyscrapers and factories we made. I figured a majority of it could be ran through some sort of block ID converter, and the rest of it patched up manually.

When going from 1.2.5 to 1.4.7, i used MIDAS Gold, but that seems to not work properly, or with data values. I also tried MC Edit 2 (which is a pain because each block has to manually be added to the list which I'm willing to do) but it seems to crash when trying to convert blocks that are added to the game. 

Does anyone have any ideas? We put a heck of allot into this server and we really want to at least carry over the buildings. I appreciate any suggestions.

Example of a couple buildings made in survival (my friends and I had nothing to do back in HS lol)
MTA HQ in development (left) - World Trade 1 (Center) - Public Workshop (right)