Yes, I listened intently to one being played yesterday at a local Mexican restaurant... I talked to the player about how good it sounded. Very resonant, very pure deep tones. He described the tuning to me, which I've since forgotten, but it's not simply an octive guitar tuning; I described 4ths and 5ths tunings with him but I don't think it meant anything to him. He did say his dad used to play tololoche, which interestingly is tuned in 4ths, but a 4th higher than double bass (ADGC).
There seem to be two sizes of guitarron, one of which sports a near gargantuan body. Unfortunately, this large body is almost eggshell fragile. To try to make an ABG of one would require some serious bracing and top reinforcement. I do believe the lowest note on the guitarron is that bottom A, just like on a toloche.