You are right. Actually here in Eastern block we had almost zero B12 cars as 99% of stock cars were built to be cheap small-engine ones with the only exception being limousines for government officials but rallying was still hugely popular sport here, definitely more than now (at least in Czechoslovakia), the same was before gr.B era. One of the reason is that rallying here in that time was really a motorsport for everybody, it was very cheap with large government support. There was a system of "leagues" where the base level was competing with almost stock cars and every advance to next level was allowed only for the successful ones.