The spacer is not that hard, you can file it down with a file while holding it in a drill if you want to. Just be sure you keep it round and centered, otherwise your regulation is apt to change as the spacer moves. If you want to try and regulate it so that it shoots parallel then you need to shoot top and bottom barrel groups. Measure the centers of both groups and then regulate it to put the barrels as far apart as the muzzles are.
On my rifle I think I set them to cross at about 50 yards with the top barrel set dead on with the sights at that distance, this will get you on a dear sized target out to at least 125 yards or better. The 06 doesn't drop that much out to 150 or so. I then set the bottom barrel to be used with the scope at longer distances. If I remember correctly I set it to be dead on at 200 yards. I don't attempt to shoot deer any farther than that and would prefer to have them much closer than that. Bob