You have asked a lot of questions, and are getting a lot of info. Let me add my two cents.
Do not be overly concerned with rifle/part numbers matching. Most all Garands went through a field or regular armory sometime in their lives so original parts are few ...if not, a rare bird indeed!
As for best load, first of all, make sure you do not overload for the Garand. Start at a minimum or medium load and work slowly up or down to get the best groups at the range. The Op-Rod is what you want to protect....I load everything for my
M1
's and I want to keep the pressure and velocity down so that I get good groups at all distances, 200-600yds. I use primarily 147-150gr bullets and work on my loads carefully, using a chronograph as I cannot test pressures. When I look at loading books, I look for books that have loads specifically for match shooting. The Accurate manual used to have a section toward the end specifically for match rounds. For the M1, I try for muzzle velocities well under 2700 fps. Remember, each new lot of powder, primers, and brass require a back to basics testing. Also, after each test load, I watch primer and brass for issues.
As you are not really clear on what use or purpose you intend for your rifle, I am not sure what to say further. If your intent is to shoot
CMP
style matches, then you should read the rule book. Many of the changes that you mention would disqualify you (muzzlebreak, synthetic stock, scope mount). Changing a barrel to a national match grade if you are not looking to be a CMP NM shooter, seems a bit like over kill.
If you are looking to go to F-CLASS, again look at the rule book. I am questioning the reason for a muzzle break? A synthetic stock is nice, but again for what purpose? Often they are much lighter than their wood counterparts, and you will get hammered in recoil.
In either case, if you are looking for info on match shooting with your M1, consider talking veteran shooters at a CMP match. Most of the seasoned veterans have been there and done it, so you will not have to reinvent the wheel.
As both a CMP match shooter and hunter, I use different rifles for each job. I consider my match rifles finely tuned instruments that I carefully take to the range. My hunting rifles, on the other hand, while I value them dearly and take care of them, I know full well that they might get dropped, banged around, etc. While I suppose that I could, I do not take any match gun into the woods.
Hope this helps.