On my bronco I thought I had a push rod length issue, I had a friend machine a longer pushrod and it didn't help I never figured out why the longer pushrod didn't do anything. I don't recall what the issue ended up being, I had tons of issues with that setup over the years. (I had a firewall tear, a bellhousing break, I think I even had a clutch fork bend, I remember re-enforcing all three...) So check your bell housing, firewall and fork too.
On our XJ my wife had it before we met, her father replaced the clutch and had a similar issue that you have. I think it was even with a LUK clutch. He told me this story after I had installed a new LUK clutch when putting the stroker in, my LUK has worked fine.
Nathan