Is this a tbi engine or vortec. The tbi engine does have center bolt valve covers but it is not a vortec. The easiest way to tell is to count the intake bolts. If it has 8 bolts that go straight down then it has vortec heads on it. If it has 12 bolts that are at a angle then it is a gen I small block. The best thing to do is to establish what your base is. There are so many different tbi engine out there. Don't forget these engine have been around now for 20 + years. I would start by getting the cast numbers off the block, heads, intake, throttle body, & injectors