I think the cover probably disintegrated. It's needed to prevent the rubber from softening up from oil exposure. I found a 1958 235 that had the complete mount on it including the cover, although it was set up for use in an earlier truck with a 47-53 bell housing. I believe you need the cover, available from the usual suspects.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.