The ONLY certain way to tell is to take a head off, but we have always found that the cross hatching/chequer finish on the hub above the modine / oil filter is the only sure way to tell from the outside.
We do see an awful lot of blocks here certainly over 1000 in 6 years oiur data is hard earned.
David APi Engines / APi Impreza
www.apiengines.com