The 835 is such a great patterning gun and there are several combinations that work very well with it.
I've seen some good patterns with the Undertaker in an 835. As far as lead shot loads go, I'd send as much down the bore as possible. Most of the time I recommend 3" shells but in this case I'd go with some Winchester 3.5" HV 2 oz. loads to get the volume that you need for that combination.
You will of course get much better patterns with H-13 but since you are looking for a lead load, that's the one I'd recommend.
Thanks,
Clark