I cannot speak to what specific length you will need as that is determined by the crank but a pair of vernier calipers can measure but I can say I would recommend getting an SKF bottom bracket in the correct size once that has been figured out. It will be a massive upgrade for the bike and not one I generally would recommend but in your case would help quite a bit. It was designed for durability and weather resistance in mind with excellent seals, stainless spindles, larger bearings including roller bearings and even has a 10 year warranty including those bearings if you should need it.