Salaam,
Well to be honest with you it is very hard to tell just by looking at the picture , it could be B16, B18, OR H22 not sure !!! any one could change the tappit cover of the engine , but one thing is for sure that it is a DOHC engine of Honda , and if the seller claims that it is a D16 series engine let him , you are getting a DOCH engine for the price of a SOHC engine .
any way i could be wrong also i lost touch with Honda engines ,since iam gathering more information on rotary engines .
bye.