The easiest way is to look and see if there is some webbing cast on the head at the No4 end.If there is then its a coscast.If its smooth then its not .The other way is to get a small mirror and look at the underside of the head just underneath No2 exhaust port....it should have COSCAST embossed into the head
the coascast heads were cast by cosworth using higher density alloy and a superior pressure casting method. No difference in power or design to some extent, except a weakness between a oil and water gallery in the rear of the later spec GM cast heads which is where the porosity problems occur.
another identifying feature is the coscast oval under number 2 exhaust port from the cambelt end.
yep it was purely cost saving. THey saved a whole bunch of cossie heads for the turbo cavaliers and calibras, 99% of these cars are coscast clad, and were produced much later than vuaxhall stopped using coscast heads on astras.