Brento,
This is actually the Atlas forum that you are in. AFAIK, Atlas never used anything but V-belts. You really should take your questions to a Forum frequented by people who own machines such as South Bend or Logan models that use or used flat belts. Receiving a valid answer to your flat belt question was just luck. I think that I can move the few posts pertaining to flat belts into one of those other Fora if you wish.
However, the other thing that you should obviously do is to go to the McMaster site and do a search on Flat Belts. That would have answered your question of how you splice or make up a flat belt.