They are not per Italian rules.
Anyway R2B and R2C are subcategories of R2 per FIA R-class rules (now replaced by the new Rally1-5 ones) and the meaning is that B has smaller engine capacity but also weight while C has larger engine and weight.
From that it looks like the Italians keep lower weight for Fiesta R2T unlike 2021 Rally4 rules which put the weight of both B and C car to the same level.