Don't forget that the T-LOC systainers are HUGELY reinforced inside the lid to handle the forces of the T-LOC fastener. This webbing/reinforcement doesn't exist on the Classic Systainers, and will create a weak point which will make them - IMHO - totally unsuited for conversion.
There are plenty of people who still find the Classic Systainers desirable- I'd suggest you sell your classics and just upgrade to T-LOC's.
I can't see a 'conversion process' turning out easy, affordable, or well...but do what you want.