Transition from CAR's to FAR's
 

After WW2 aeroplanes were certificated under the CAR 4a (below 12,500lbs) and CAR 4b (bigger stuff). As times changed the regulations became the FAR Part 23 (small aircraft) and 25 (Transport).
But CAR 4a held within itself "Normal" and "Transport" Categories, while 4b was all "Transport".
So when the rules were changed to the FAR's how were the 4a Transport Category aircraft transitioned?
Is an old CAR 4a Transport Category aircraft grandfathered into Commuter Category due to weight, or into FAR 25 due to "Transport"?