First of all: DAMN!
Secondly: major kudos to you for taking in this poor abused snake. I've never heard of using snakes as 'drug mules' but, I'm sure these scum would try anything.
I did a quick Google search and found an article that mentions using boa constrictors as mules. You can read it here: Snakes and Illegal Drugs
From the above mentioned article:
"On June 29th, 1993, Drug Enforcement Agents at Miami airport found 36 kilos of cocaine wrapped in condoms and stuffed into Boa constrictors, Boa constrictor. The snakes, imported from South America, were still alive when found, and consisted of 312 animals averaging about 1.5 metres in length. The cocaine was only found by accident when one of the snakes was seen to have an unnatural bulge. Officials X-rayed it to see what was inside and removed two condom-wrapped pellets, each containing four ounces of cocaine. Despite observation the officials were unable to apprehend anyone in relation to the case. They were also unable to find the importer and no arrests or charges were laid. It was the largest discovery of drugs in snakes ever."
Lastly: 20-30 years is generally listed as a safe estimate. (Although the oldest on record passed at 47.)
Please be sure to read over the excellent Ball Python Care Sheet located on this site.
Good luck with your new buddy, and may you both enjoy many happy years together.