When my 6AL took a dump the engine would backfire at 1st then the poping at around 3k. Then the box died. I sent it to MSD and they fixed the problem for 40 sumthing bux plus shipping. I carry a spare now. Either in the boat or in my Truck.
BAd Ground got mine. You need to remove the connection and clean it once in a while.
Try this link
Take the coil wire off and place it close to a ground and touch the white wire to a ground and you should get a spark if the box is ok. If your dist. has some age on it you may want to check it.here... this is the docs on the 6AL box, it has the testing instructions in it.
I tryed turning the rotor bug by nand while the dist was still in the motor and it did not turn. that what got me to think that the chain brokethat sucks at least you didn't waist a couple hundred bucks on a new box!
Pull the valve covers and see if the rockers are moving while sombody's crankin. Your sure that the gear pin on the dist didnt snap? Check it! Tap it out and see, might as well before you go digging into the motor.