Is there a trick to getting these on the carb when they get old and hard? Just put a new top end back on and this is holding me up. I have considered just putting a pod filter on it but not sure how well those work for normal driving on these engines.

Heat - either gently from a gun (I've got a broken hair dryer that does the trick), or putting in boiling water.

Be aware, though, that they do shrink over the years so, even when softened up, might still be a struggle. Have a look to see if Clauss Studios or KDI do new ones for your model.