I just dealt with this particular issue after removing a pinned muzzle brake from my BM 1/7 GI-profile bbl in post-Sunset glee. I never used a crush washer before and didn't know what to expect, and I found these things don't crush easily. My A2 birdcage was about 270° away from TDC and it was going to take an INSANE amount of torque to get it moving; like timing-an-FAL-barrel kind of torque. It wouldn't budge and I didn't think all this effort should be necessary. Plus, I don't have barrel blocks (only a receiver block) and I had significant concerns that the amount of torque I would have applied would have sheared my barrel index pin, or at least enlarged the index pin slot in the upper.
I tried pre-crushing the washer in a vice as suggested above, and no luck. It would NOT pre-crush.
My solution: treat the crush washer like a peel washer. I filed down the washer (on the barrel side) a smidge at a time, checking the FH timing as I went. It was very easy to keep the filing perfectly smooth and even by dragging the washer along a flat file - no burrs or file marks. At about 90° to go, I took a little off the other side of the washer, bringing me to 45° within TDC (about 10:30 timing). From this point, I torqued the FH down, bringing the top slot to 12:00. This provided a significant but by no means excessive amount of torque, and I have no concerns about the FH coming loose.
I've read excessive torque on the muzzle device can cause accuracy problems; I later used this barrel/FH combo to shoot the best 20-shot, open-sight 200 yard group of this barrel's (and possibly my) life.
My two cents: I think barrel blocks are required for "proper" FH installation using a crush washer. Don't stress that upper/index pin interface.