Start looking for a set of lock bar sights. Just about all of the M1s coming out of the CMPicon will have the post war style sights.

If the rifle you end up with has a stamped trigger guard, consider changing it to a milled trigger guard. The stamped came out late in the War. If you want to be authentic for all parts of the war you will need a milled trigger guard.

Also check the gas cylinder lock. You need the rounded top version instead of the post war version with the square "hump".

Good Luck
Mark Hubbs (former WWII reenactor)