a type of hair cut guys get

I have a 33 LP Willie Nelson Album jacket circa 1960; Willie has a crew-cut.

You don't flat top a crew cut. You can have either a flat top or a crew cut. A flat top is a type of a crew cut. Normally a #1 is used on the sides of the head up to the crest. the top is cut in such a way that when styled straight up it forms a straight line across the top. Also normally the very front of the hair (the bangs area) is slightly longer and styled straight up also.

Presumably the 1890s

Crew cut sweaters may be purchased from department stores like Walmart. You may also order these online however you have to pay for shipping and handling.