IMHO, if your looking for no more power then ports are far too big, I've got a much much smaller head than that on the ports and it gave 303bhp on a 1600cvh

Id say that head is your weak point, also standard valves are fine for 300bhp on a 1600 obviously the 2.0l zvh will need more flow but the head looks poor, I can't get over the sizeof the port at the start its huge!