Don't say you're attempting to start modifying a Tekin conversion kit!
My god man leave it alone, if you want to rearrange the batteries put the Tekin kit on ebay and buy a sheet of carbon fibre with your profits.
The Tekin chassis was fairly well balanced as it was, not many people used it as it didn't put as much weight on the rear as the stock chassis with the rear mounted motor. Rather than ask what to do about the battery arrangement now, surely it would be sensible to run it first and see how it handles?
Use the mounting holes that are already in the chassis to mount the T4 front end, start drilling your own holes in the chassis and it will be worth nothing.