My 80's Gitane was set up this same way. If your ride is anything like mine, the Aria drum brake is just not very good at stopping quickly, and the right lever controlling both front and rear rim brakes needs a lot of effort to put enough force on the brake lever to effect a quick stop. Depending on the location of your shifters, if you're not using bar-end shifters, you might try putting the drum on a bar-end shift lever and separate the front rim brake to the left lever and rear rim brake to the right lever (unless you're located in England or similar locale). If you are using bar-end shifters, some have given the drag brake duties to the stoker with the understanding that it will only be used at the direction of the captain unless going straight.
The convensional wisdom is that the drum brake is only really useful as a drag brake when traversing down long hills, and you wish to keep your speed down without overheating the rims. The drum brake is capable of absorbing a lot of heat.
If you wish to keep the brake setup as is, I recall that the right lever has a special adapter built in that allows two normal cable ends to fit in right next to each other. Only the rear needs to be of tandem length, as the front rim brake is a short run, just as any other normally configured upright bicycle.
Hope that helps.