Trial and error...Here's what I finally did.
The stack for the evaporator was 8". I took an 7" diameter piece of stove pipe and wrapped the copper around the smaller pipe. As it was hard to bend the tubing tight to the pipe, by the time this was done it just had to be sprung slightly to slip it over the 8" pipe.
The preheater was 2 - 25' runs of tubing. I straightened them out and laid them on the floor, used small band clamps to hold them together, and rolled the pipe along the floor and coiled the tubing around.