Toilet installation in raised foundation concrete floor

Here's my problem. I live in house with a raised foundation built in 1928. The bathroom floor is a 4" thick concrete pad. Over the years the shower pan has leaked and also the water closet flange rotting the wood. I've removed the floor in the shower pan and will replace with plywood and mortar. I think I will have to remove a portion of the bathroom floor and replace with new concrete doweled into remaining floor.

My problem is I need to replace the cast iron drain. ABS is fine with me but how do I fasten it to the concrete. Someone tells me I have to use lead. Any hlep would be appreciated.