I had the same problem with my 28 - tried everything from rubber mallet to MMO ended up grinding outer tab to remove levers,split rivits to separate 2 mounting halves and found problem - one of the "babbit" balls on one side was in almost a million peices and one on the other side was split in two. hopefully this is not your problem as well. when I find replacement balls I was just going to re-rivit the 2 halves back together and tack weld the levers to the cross shafts
27 speedster, 28 coupe, 67 camaro, 67 p/u, 75 vega and now 1920 490