4AFC = 1600 twincam 16v carby, Inlet cam is run from gear under the cam cover and the exhaust is run from the belt.
I had the same engine in my AE82 seca, Had a cold air intake and a full exhaust and did a 17.9 quarter mile pass. Wasn't the quickest car on the road but it was fun.
6A and 4A are the same except the 6A has 76mm bore and 77mm stroke.