5-6 in my usual configuration but with a unlined lanyard hole with countersunk smooth edges. I believe I have seen such a lanyard hole on older #14-15's in one of the books.

Another feature would be a canteen snap on the sheath.. I owned a knife with a canteen snap sheath and it just seemed easier to close while on the hip.

As far as vintage, a new a WW2 era 1-7 with a brand new period sheath would really be something special. Reading the first few chapters of the Gaddis book really makes me wish I could order one.