Ok so today i finally got to compare a B18A1 head with the B20A head. The cams are almost exact the only differences are cam gear side is about 1/16-2/16ths longer offsetting the cam gear a little but it appears not to cause a problem. Second the exhaust cam does not have th grove for the sensor. So B18A1 cams will work with minor adjustments and if you wanted you would only have to have the grove cut in by a machine shop. As for valve
B18A1exh,B20A int cams
And for valves the intake valves are an exact match but the B20A exhaust valves a bit larger. I have to check with my machinist on this but i would imagine most companies sell oversized valves but i would imagine you will need head work if you do this. But i imagine most if any would only be interested in better cams in anything but i need the valve train done for my turbo setup.
Just a few other pics: