you will see variations of the mounts as well for all my sixes. i have got two mounts at once one had one size mounting threads the other had a smaller one. some have been slightly thicker than the other one. some of the big truck 292's had a thicker mount that was square. i only remove 8's never put them back in. hahaha. you have lifted the block and bolted mount to it and the whole thing won't lower down right? can you start one side and pry on it while letting block down? it may just want to be a pain no matter what. you might try to wait till it's very cold and uncomfortable that's when i always have to always pull/ install a engine.