If you are using older heads, the 351Ws have more intake bolt holes. These are there solely for your amusement and you can ignore them. Weiand seems to be the only aftermarket company that ever bothered including provision for these extra bolts holes, nobody else ever bothered. Nor should they bother you. The later heads (1975 and newer IIRC) didn't have extra bolt holes.
You'll have water passages in the ends of the heads that are either "square" or "L-shaped". On some gasket kits they include both types. Others just include the square types. The square ones work either way, the L kind can be trimmed a bit if needed and be made to macth a square opening. You can ignore the port of the intake, just how the ones on the heads are made is important.
If you don't want to use headbolt shims you can buy "stepped" headbolts from ARP that are purpose made to bolt 351W heads onto 289/302's. Shims are cheaper but ARP bolts are top quality. Either way works though.