If you have a caliper, measure the diameter of the op-rod piston head. It should not be less than 0.525". Anything less, you may have short-cycling problem. It would be nice to know the throat erosion of the barrel. But it may not be possible. I personally think the throat erosion is not as important as the muzzle erosion, esp. for a shooter grade M1. M1 must be cleaned from the muzzle. Hence, using the GI steel jointed cleaning rod, soldiers cleaning the M1 in the old days may have caused some uneven wear on the muzzle crown. Take a 30 cal M2 ball and drop it down the muzzle upside down. The M2 ball has the cannelure a bit lower than the standard 150 grain 308 ball. Then inspect how much of the bullet still showing beyond the muzzle end. If it is less than 1/8", I would not take it. The more the bullet sticks out, the better the muzzle condition. I have an ex Korean M1 garand with a pitted and sewer pipe looking bore. I guess the Korean army conscript did not care to clean their rifles that much. But the rifle still shoots really well (and have taken a few top places in Garand matches in the state). Because they did not clean it much, the muzzle is tight ... really tight. And this contributes to its accuracy.
If you see any ding or scratch on the muzzle end, but the bore looks good, you may be able to have a competent gunsmith to put a new crown on the old barrel.
Good hunting.
oz