Hi and welcome to mightyram. Being a 92' truck it won't be a 2.6 so unless it's a V6 it'll be a 4G64 (2.4 L) Check engine light could be a number of things but you can get error codes off the ECU by plugging in an OBD 1 scanner and it will reveal all. The oil leak is probably something as minor as a bad rocker cover gasket.