I think the biggest reason for the increase in pattern spread comes not necessarily from the fiber wads themselves (though the certainly don provide the cushion that the most plastic wads do), but from the lack of a protective shot cup. Back in the old days (I'm dating myself, to be sure), Remington's "Power Piston" was a great advancement in shot shell technology. From the early 1960s onward, the advances to shotshells have minimized pellet damage and tightened patterns. Back then, a constriction of .040 was considered full choke, today that's extra full.
The lack of a shot cup exposed pellets to damage from bore scrubbing, which flattened the sides, created more flyers and opened patterns. If you reload, try cutting off the petals of your wads and use chilled (not magnum) shot. Using a faster powder will also tend to open the pattern some.
Or, you could just get some spreader loads!