These are the original GT40 heads with bronze freeze plugs and inserts (1991 and up HO Ford 351W).
302 and 351 Windsor Heads are interchangable, 302 head bolt holes must be drilled slightly for 351 head bolts. If using 351 heads on a 302 special bolts are available from auto parts store.
For carbureted engines the GT40 "P" (automotive 302) head is a nice alternative to the GT40. If using "P" heads in salt water it is recommended to replace the freeze plugs with brass.