Hi, 7.62 and Oleg,
Why do people always make putting together a rifle from a kit sound so simple?
If the new receiver is one of those made for Century Arms, you might want to read the information on
http://www.fulton-armory.com.
There is always a potential problem with installing a used barrel on a rifle like the M1. New barrels are short chambered, that is they are made with too little headspace. When a new barrel is installed, a try bolt (actually a gauge, not any old bolt) is used, or the original bolt is used, and the chamber reamed to the correct headspace. With a used barrel, headspace may be too short, in which case the reamer can be used, or too long. If it is too long, a number of bolts can be tried to see if one will bring headspace within specifications. If this fails, a new barrel is the only solution.
(Anyone who says, "Oh, just set the barrel back" probably does not know what he is talking about. The common practice with sporting rifles of cutting the barrel and setting it back one thread will not work with the M1 because the barrel would then be too short and that would destroy the relationship between the barrel and the operating rod as well as the stock fittings, etc.)
In addition, the M1 does not have witness marks, so a gadget called a "barrel timing gauge" must be used to get the barrel lined up and make sure the front sight and gas cylinder are in proper alignment with the receiver. (This is not merely to get the right sight picture - the gas cylinder and operating rod must be lined up properly with the receiver or the op rod may jump out of its track.)
BTW, insufficient headspace is always adjusted by reaming the chamber. Grinding the locking lugs can be done, but is very poor practice and I would question the ability of any gunsmith who recommended it.
Jim