You'd probably have to look at the build sheet. In line 4 (build codes) you will find boxes under EXHAUST and TAIL PIPE for the LT and RT side part numbers(last 2 or 3 PN digits). If they are both filled in you have dual exhaust. The 73 Charger I had has 000 for the left side under EXHAUST and it was a single exhaust car. Under exhaust mine has 945(LT) and 672(RT) and under tail pipe 02(LT) and 03(RT). Tail pipe part numbers 3466102 and 3466103.
In line 11 (sales codes) you will see under ENGINE ACCESSORIES(sales code N) 2 boxes. One vertically labeled EXHAUST and the other beside it vertically labeled EXHAUST TIPS. Both will have a 4 followed by a dash and have a box below with typed in digits. My 74 has a 1 under EXHAUST for N41 (Dual Exhaust)and a 2 under EXHAUST TIPS for N42 (Chrome Exhaust Tips). The sales car selector book has a statement in the Satellite section under "New for 74", "All V-8 engines with dual exhaust come with bright tips. I don't know if that was also true for Chargers as well.