That exact thing is something that always bugged me, the fact that you could use the same "35t right arm" structure to replace the arm of a Jenner and of a wolfhound despite their designs being so vastly different. It would add a great deal of realism if there were some mechs with identical or nearly identical limbs/torsos so you could use the same spare parts and for others you would have to carry extra stuff, because the designs are too different.
And about Weapons form different manufacturers having different stats, i really like that idea. Lets try it with the AC/2 because there are only 4 models:
Imperator Smoothie-2:
Has extremely precise rangefinder and recoil handling and is therefore more precise than the competitor models, but also bigger and slower to aim, which is a disadvantage at closer ranges.
Stats: 1 more crit slot, minimum range of 6, other ranges are 9 - 18 - 27
Mydron D:
Fast tracking, minimum range reduced to 2. Also easy to repair ( +2 to maintenance checks)
Zeus Bolt:
Has the capability to be rapidfired, when doing so it deals 3 damage, genreates double heat, uses 2 ammo and has +1 to hit.
Whirlwind:
Instead of focusing fire on a single point, this weapon spreads its shells over a larger area, which makes enemies easier to hit, but it eats through ammunition faster, is heavier and less precise than its competitors.
Stats: same minimum range, other ranges: 7-14-21, half a ton heavier, always uses 2 ammo, -1 to hit.
Those are just some examples that i could think of the top of my head, probably not very balanced.
Would someone be interested in weaponprofiles for every weapon?