OP,

We used to pull engine sleeves out of model airplane engines by heating them up in the oven to 350 degrees,
the sleeve would just slip right out. At room temp they wouldn't budge. Same for install. The engines where aluminum
housings with crome lined brass sleeves.

Try heating the upper/rail to somewhere about 250-350 and give the screw a crank. I don't think it will harm any of
the parts. Matter of fact, I just installed a tight barrel into an upper a few weeks ago this way, slid right in and locked
right in place.