Unfortunately you are SOL with a better FM antenna unless you can find a used one. All the Winegard 6055's seem to have disappeared.
Not sure how much a modified FM6 will help you, but it's easy enough to do. The modification will improve the front to back ratio, but doesn't add any forward gain so it's hard to say how much improvement you will actually see.
Are you having trouble at certain times, or all the time? The atmosphere is still quite active with
tropospheric activity, but will start simmering down as cooler weather moves in. The tropo activity can really wreak havoc on normally decent reception when signals from 200+ miles on the same frequency override them.