MAD ammeter bypass question

Yep. Not sure where the 7.5 amp number you are using comes from. The single stock 6” 16ga fusible link should open with prolonged exposure to around 30-40 amps or so with a dead short in any of the stock unfused wiring or components. Parallelling the stock fusible 16ga link with another 14-12 ga fusible link (50-60amps to open) means it will take close to 100 amps to open both fusible links and stop current flow. Look up Kirchhoff's current law and the current divider rule. Using rough numbers here, exact numbers depend on just what the voltage drop ends up being across both legs of the parallel circuit from the point of the short circuit. Either way, the stock 12ga wiring won’t take anywhere near that kind of current, effectively no circuit protection at all, may as well not have any circuit protection on the shunt wire, wires will still burn.