Split Bus Panel

Hi All A few questions about Split Bus Panels. Looking at finishing a residental basement. Located in NJ. House has a split bus panel which is a Murray. The panel has 4 double pole breakers in the top half in the service disconnect area. They are 40amp (range), 40amp (AC), 30 amp (dryer - not used) and 60amp (Lighting+everything else). House also has a redundant hot water circuit on a separate meter (not live). The lower branch section has around 8 breaker positions - top six will take 1/2" according to the panel label. Furnace is NG. 70amp breaker rating max for the entire panel. First question: The panel says 125 amps load for the top positions. Installed breakers total 170amps currently. I've read various discussions around whether the total of the breakers in the upper section can exceed the panel rating or not. A rough load calc says its currently ok but clearly if everything was used to the max rating on the installed breakers it would exceed 125 amps. What is the correct approach here ?