The 351W with its significantly higher deck height can be distinguished by looking at the height of the front lifter valley rail. IIRC, the 351W is about 3/4-1" higher than the 302 in this area. The 351W also 1/2" head bolts as opposed to the 302's 7/16" bolts. If there are 351 heads on it and it has stepped bolts, or special insert washers to utilize the 7/16" bolts, then its not a 351W.