Sorry for your loss.
I have built a 500 counterflow, a 250 offset and a 60 counterflow. I too am getting older and will be selling the 500 but I love the size of the 60. I will follow along as you progress.
I worked in the Propane industry and tanks were free (the best kind).
I have attached a photo of the 60.
I would be happy to discuss any thing about it if you would like. Feel free to contact me.