I realize checking alignment is probably something that should be done on any sled but why would it change without loosening the front mag side mount when swapping mounts out? Variations/inconsistencies in new mounts? I swapped mine and was still within spec.
x2 not to mention the amount these are out when the motor mounts are actually clapped out, I don't think the manufacturing tolerances on the new inserts are going to be very far off of what the old ones were, and as long as it was close from the factory, I don't see a reason to worry about it if you change them one by one as you are FAR BETTER off than when you started. And this is coming from a machinist by trade who can talk numbers until your ears bleed. Snowmobiles are not precise machines. Get those new inserts in there and run er