Sad truth is, classic helmets are shit. This topic came up recently and was discussed in great detail, if I recall correctly. I love the look of an old Bell full face, but if you find one at a swap meet, check out the guts -- HARD styrofoam, that's IF you can find one that isn't dry rotted all to hell.
Do yourself a favor and get some nice, modern, safe, cushy protection for yer bean.
Go to a local bike shop and try some different ones on. A helmet that looks cool but doesn't fit or won't protect well is an exercise in futility.
A friend told me that everyone has either an "Arai head" (a.k.a. oval) or a "SHOEI head" (a.k.a. round). Turns out I've been wearing Shoei's all along when I'm really an Arai head. Go figure.
Honda go sideways!